Implementing BGP

Border Gateway Protocol (BGP) is an Exterior Gateway Protocol (EGP) that allows you to create loop-free interdomain routing between autonomous systems. An autonomous system is a set of routers under a single technical administration. Routers in an autonomous system can use multiple Interior Gateway Protocols (IGPs) to exchange routing information inside the autonomous system and an EGP to route packets outside the autonomous system.

This module provides conceptual and configuration information on BGP.

BGP Functional Overview

BGP uses TCP as its transport protocol. Two BGP routers form a TCP connection between one another (peer routers) and exchange messages to open and confirm the connection parameters.

BGP routers exchange network reachability information. This information is mainly an indication of the full paths (BGP autonomous system numbers) that a route should take to reach the destination network. This information helps construct a graph that shows which autonomous systems are loop free and where routing policies can be applied to enforce restrictions on routing behavior.

Any two routers forming a TCP connection to exchange BGP routing information are called peers or neighbors. BGP peers initially exchange their full BGP routing tables. After this exchange, incremental updates are sent as the routing table changes. BGP keeps a version number of the BGP table, which is the same for all of its BGP peers. The version number changes whenever BGP updates the table due to routing information changes. Keepalive packets are sent to ensure that the connection is alive between the BGP peers and notification packets are sent in response to error or special conditions.


Note


VPNv4 address family is supported effective from Cisco IOS XR Release 6.1.31. However, VPNv6 and VPN routing and forwarding (VRF) address families will be supported in a future release.

Enable BGP Routing

Perform this task to enable BGP routing and establish a BGP routing process. Configuring BGP neighbors is included as part of enabling BGP routing.


Note


  • At least one neighbor and at least one address family must be configured to enable BGP routing. At least one neighbor with both a remote AS and an address family must be configured globally using the address family and remote as commands.

  • When one BGP session has both IPv4 unicast and IPv4 labeled-unicast AFI/SAF, then the routing behavior is nondeterministic. Therefore, the prefixes may not be correctly advertised. Incorrect prefix advertisement results in reachability issues. In order to avoid such reachability issues, you must explicitly configure a route policy to advertise prefixes either through IPv4 unicast or through IPv4 labeled-unicast address families.


Before you begin

BGP must be able to obtain a router identifier (for example, a configured loopback address). At least, one address family must be configured in the BGP router configuration and the same address family must also be configured under the neighbor.


Note


If the neighbor is configured as an external BGP (eBGP) peer, you must configure an inbound and outbound route policy on the neighbor using the route-policy command.


Procedure


Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

route-policy route-policy-name

Example:


RP/0/RP0/CPU0:router(config)# route-policy drop-as-1234
  RP/0/RP0/CPU0:router(config-rpl)# if as-path passes-through '1234' then
  RP/0/RP0/CPU0:router(config-rpl)# apply check-communities
  RP/0/RP0/CPU0:router(config-rpl)# else
  RP/0/RP0/CPU0:router(config-rpl)# pass
  RP/0/RP0/CPU0:router(config-rpl)# endif
  

(Optional) Creates a route policy and enters route policy configuration mode, where you can define the route policy.

Step 3

end-policy

Example:


RP/0/RP0/CPU0:router(config-rpl)# end-policy

(Optional) Ends the definition of a route policy and exits route policy configuration mode.

Step 4

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.

Step 5

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters mode.

Step 6

router bgp as-number

Example:


RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the BGP AS number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 7

bgp router-id ip-address

Example:


RP/0/RP0/CPU0:router(config-bgp)# bgp router-id 192.168.70.24

Configures the local router with a specified router ID.

Step 8

address-family { ipv4 | ipv6 } unicast

Example:


RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 unicast

Specifies either the IPv4 or IPv6 address family and enters address family configuration submode.

To see a list of all the possible keywords and arguments for this command, use the CLI help (?).

Step 9

exit

Example:


RP/0/RP0/CPU0:router(config-bgp-af)# exit

Exits the current configuration mode.

Step 10

neighbor ip-address

Example:


RP/0/RP0/CPU0:router(config-bgp)# neighbor 172.168.40.24

Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address as a BGP peer.

Step 11

remote-as as-number

Example:


RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 2002

Creates a neighbor and assigns a remote autonomous system number to it.

Step 12

address-family { ipv4 | ipv6 } unicast

Example:


RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family ipv4 unicast

Specifies either the IPv4 or IPv6 address family and enters address family configuration submode.

To see a list of all the possible keywords and arguments for this command, use the CLI help (?).

Step 13

route-policy route-policy-name { in | out }

Example:


RP/0/RP0/CPU0:router(config-bgp-nbr-af)# route-policy drop-as-1234 in

(Optional) Applies the specified policy to inbound IPv4 unicast routes.

Step 14

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Enabling BGP: Example

The following shows how to enable BGP.


  prefix-set static
     2020::/64,
     2012::/64,
     10.10.0.0/16,
     10.2.0.0/24
  end-set
  
  route-policy pass-all
    pass
  end-policy
  route-policy set_next_hop_agg_v4
    set next-hop 10.0.0.1  
  end-policy
  
  route-policy set_next_hop_static_v4
    if (destination in static) then
      set next-hop 10.1.0.1
    else
      drop
    endif
  end-policy
  
  route-policy set_next_hop_agg_v6
    set next-hop 2003::121
  end-policy
  
  route-policy set_next_hop_static_v6
    if (destination in static) then
       set next-hop 2011::121
    else
       drop
    endif
  end-policy
  
  router bgp 65000
    bgp fast-external-fallover disable
    bgp confederation peers
      65001
      65002
    bgp confederation identifier 1
    bgp router-id 1.1.1.1
    address-family ipv4 unicast
      aggregate-address 10.2.0.0/24 route-policy set_next_hop_agg_v4
      aggregate-address 10.3.0.0/24 
      redistribute static route-policy set_next_hop_static_v4
    address-family ipv6 unicast
      aggregate-address 2012::/64 route-policy set_next_hop_agg_v6
      aggregate-address 2013::/64
      redistribute static route-policy set_next_hop_static_v6
   			neighbor 10.0.101.60
      remote-as 65000
      address-family ipv4 unicast
      neighbor 10.0.101.61
      remote-as 65000 
      address-family ipv4 unicast
      neighbor 10.0.101.62
      remote-as 3
      address-family ipv4 unicast
        route-policy pass-all in
        route-policy pass-all out
      neighbor 10.0.101.64
      remote-as 5
      update-source Loopback0
      address-family ipv4 unicast
        route-policy pass-all in
        route-policy pass-all out
      

Adjust BGP Timers

BGP uses certain timers to control periodic activities, such as the sending of keepalive messages and the interval after which a neighbor is assumed to be down if no messages are received from the neighbor during the interval. The values set using the timers bgp command in router configuration mode can be overridden on particular neighbors using the timers command in the neighbor configuration mode.

Perform this task to set the timers for BGP neighbors.

Procedure


Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:


RP/0/RP0/CPU0:router(config)# router bgp 123

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

timers bgp keepalive hold-time

Example:


RP/0/RP0/CPU0:router(config-bgp)# timers bgp 30 90

Sets a default keepalive time and a default hold time for all neighbors.

Step 4

neighbor ip-address

Example:


RP/0/RP0/CPU0:router(config-bgp)# neighbor 172.168.40.24

Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address as a BGP peer.

Step 5

timers keepalive hold-time

Example:


RP/0/RP0/CPU0:router(config-bgp-nbr)# timers 60 220

(Optional) Sets the keepalive timer and the hold-time timer for the BGP neighbor.

Step 6

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Change BGP Default Local Preference Value

Perform this task to set the default local preference value for BGP paths.

Procedure


Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:


RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

bgp default local-preference value

Example:


RP/0/RP0/CPU0:router(config-bgp)# bgp default local-preference 200

Sets the default local preference value from the default of 100, making it either a more preferable path (over 100) or less preferable path (under 100).

Step 4

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Configure MED Metric for BGP

Perform this task to set the multi exit discriminator (MED) to advertise to peers for routes that do not already have a metric set (routes that were received with no MED attribute).

Procedure


Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:


RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

default-metric value

Example:


RP/0/RP0/CPU0:router(config-bgp)# default-metric

Sets the default metric, which is used to set the MED to advertise to peers for routes that do not already have a metric set (routes that were received with no MED attribute).

Step 4

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Configure BGP Weights

A weight is a number that you can assign to a path so that you can control the best-path selection process. If you have particular neighbors that you want to prefer for most of your traffic, you can use the weight command to assign a higher weight to all routes learned from that neighbor. Perform this task to assign a weight to routes received from a neighbor.

Procedure


Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:


RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

neighbor ip-address

Example:


RP/0/RP0/CPU0:router(config-bgp)# neighbor 172.168.40.24

Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address as a BGP peer.

Step 4

remote-as as-number

Example:


RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 2002 

Creates a neighbor and assigns a remote autonomous system number to it.

Step 5

address-family { ipv4 | ipv6 } unicast

Example:


RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family ipv4 unicast

Specifies either the IPv4 or IPv6 address family and enters address family configuration submode.

To see a list of all the possible keywords and arguments for this command, use the CLI help (?).

Step 6

weight weight-value

Example:


RP/0/RP0/CPU0:router(config-bgp-nbr-af)# weight 41150

Assigns a weight to all routes learned through the neighbor.

Step 7

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


What to do next

You the clear bgp command for the newly configured weight to take effect.

Tune BGP Best-Path Calculation

BGP routers typically receive multiple paths to the same destination. The BGP best-path algorithm determines the best path to install in the IP routing table and to use for forwarding traffic. The BGP best-path comprises of three steps:
  • Step 1—Compare two paths to determine which is better.

  • Step 2—Iterate over all paths and determines which order to compare the paths to select the overall best path.

  • Step 3—Determine whether the old and new best paths differ enough so that the new best path should be used.


Note


The order of comparison determined by Step 2 is important because the comparison operation is not transitive; that is, if three paths, A, B, and C exist, such that when A and B are compared, A is better, and when B and C are compared, B is better, it is not necessarily the case that when A and C are compared, A is better. This nontransitivity arises because the multi exit discriminator (MED) is compared only among paths from the same neighboring autonomous system (AS) and not among all paths. BGP Best Path Algorithm provides additional conceptual details.
Perform this task to change the default BGP best-path calculation behavior.

Procedure


Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:


RP/0/RP0/CPU0:router(config)# router bgp 126

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

bgp bestpath med missing-as-worst

Example:


RP/0/RP0/CPU0:router(config-bgp)# bgp bestpath med missing-as-worst

Directs the BGP software to consider a missing MED attribute in a path as having a value of infinity, making this path the least desirable path.

Step 4

bgp bestpath med always

Example:


RP/0/RP0/CPU0:router(config-bgp)# bgp bestpath med always

Configures the BGP speaker in the specified autonomous system to compare MEDs among all the paths for the prefix, regardless of the autonomous system from which the paths are received.

Step 5

bgp bestpath med confed

Example:


RP/0/RP0/CPU0:router(config-bgp)# bgp bestpath med confed

Enables BGP software to compare MED values for paths learned from confederation peers.

Step 6

bgp bestpath as-path ignore

Example:


RP/0/RP0/CPU0:router(config-bgp)# bgp bestpath as-path ignore

Configures the BGP software to ignore the autonomous system length when performing best-path selection.

Step 7

bgp bestpath compare-routerid

Example:


RP/0/RP0/CPU0:router(config-bgp)# bgp bestpath compare-routerid

Configure the BGP speaker in the autonomous system to compare the router IDs of similar paths.

Step 8

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Set BGP Administrative Distance

An administrative distance is a rating of the trustworthiness of a routing information source. In general, the higher the value, the lower the trust rating. Normally, a route can be learned through more than one protocol. Administrative distance is used to discriminate between routes learned from more than one protocol. The route with the lowest administrative distance is installed in the IP routing table. By default, BGP uses the administrative distances shown in here:
Table 1. BGP Default Administrative Distances

Distance

Default Value

Function

External

20

Applied to routes learned from eBGP.

Internal

200

Applied to routes learned from iBGP.

Local

200

Applied to routes originated by the router.


Note


Distance does not influence the BGP path selection algorithm, but it does influence whether BGP-learned routes are installed in the IP routing table.


Perform this task to specify the use of administrative distances that can be used to prefer one class of route over another.

Procedure


Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:


RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

address-family { ipv4 | ipv6 } unicast

Example:


RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 unicast

Specifies either an IPv4 or IPv6 address family unicast and enters address family configuration submode.

To see a list of all the possible keywords and arguments for this command, use the CLI help (?).

Step 4

distance bgp external-distance internal-distance local-distance

Example:


RP/0/RP0/CPU0:router(config-bgp-af)# distance bgp 20 20 200

Sets the external, internal, and local administrative distances to prefer one class of routes over another. The higher the value, the lower the trust rating.

Step 5

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Indicate BGP Back-door Routes

In most cases, when a route is learned through eBGP, it is installed in the IP routing table because of its distance. Sometimes, however, two ASs have an IGP-learned back-door route and an eBGP-learned route. Their policy might be to use the IGP-learned path as the preferred path and to use the eBGP-learned path when the IGP path is down.

Perform this task to set the administrative distance on an external Border Gateway Protocol (eBGP) route to that of a locally sourced BGP route, causing it to be less preferred than an Interior Gateway Protocol (IGP) route.

Procedure


Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:


RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

address-family { ipv4 | ipv6 } unicast

Example:


RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 unicast

Specifies either the IPv4 or IPv6 address family and enters address family configuration submode.

To see a list of all the possible keywords and arguments for this command, use the CLI help (?).

Step 4

network { ip-address / prefix-length | ip-address mask } backdoor

Example:


RP/0/RP0/CPU0:router(config-bgp-af)# network 172.20.0.0/16 

Configures the local router to originate and advertise the specified network.

Step 5

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Back Door: Example

Here, Routers A and C and Routers B and C are running eBGP. Routers A and B are running an IGP (such as Routing Information Protocol [RIP], Interior Gateway Routing Protocol [IGRP], Enhanced IGRP, or Open Shortest Path First [OSPF]). The default distances for RIP, IGRP, Enhanced IGRP, and OSPF are 120, 100, 90, and 110, respectively. All these distances are higher than the default distance of eBGP, which is 20. Usually, the route with the lowest distance is preferred.

Router A receives updates about 160.10.0.0 from two routing protocols: eBGP and IGP. Because the default distance for eBGP is lower than the default distance of the IGP, Router A chooses the eBGP-learned route from Router C. If you want Router A to learn about 160.10.0.0 from Router B (IGP), establish a BGP back door. See .

In the following example, a network back-door is configured:


RP/0/RP0/CPU0:router(config)# router bgp 100
RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-af)# network 160.10.0.0/16 backdoor

Router A treats the eBGP-learned route as local and installs it in the IP routing table with a distance of 200. The network is also learned through Enhanced IGRP (with a distance of 90), so the Enhanced IGRP route is successfully installed in the IP routing table and is used to forward traffic. If the Enhanced IGRP-learned route goes down, the eBGP-learned route is installed in the IP routing table and is used to forward traffic.

Although BGP treats network 160.10.0.0 as a local entry, it does not advertise network 160.10.0.0 as it normally would advertise a local entry.

Configure Aggregate Addresses

Perform this task to create aggregate entries in a BGP routing table.

Procedure


Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:


RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

address-family { ipv4 | ipv6 } unicast

Example:


RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 unicast

Specifies either the IPv4 or IPv6 address family and enters address family configuration submode.

To see a list of all the possible keywords and arguments for this command, use the CLI help (?).

Step 4

aggregate-address address/mask-length [ as-set ] [ as-confed-set ] [ summary-only ] [ route-policy route-policy-name ]

Example:


RP/0/RP0/CPU0:router(config-bgp-af)# aggregate-address 10.0.0.0/8 as-set

Creates an aggregate address. The path advertised for this route is an autonomous system set consisting of all elements contained in all paths that are being summarized.

  • The as-set keyword generates autonomous system set path information and community information from contributing paths.

  • The as-confed-set keyword generates autonomous system confederation set path information from contributing paths.

  • The summary-only keyword filters all more specific routes from updates.

  • The route-policy route-policy-name keyword and argument specify the route policy used to set the attributes of the aggregate route.

Step 5

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Understanding BGP MD5 Authentication

BGP provides a mechanism, known as Message Digest 5 (MD5) authentication, for authenticating a TCP segment between two BGP peers by using a clear text or encrypted password.

MD5 authentication is configured at the BGP neighbor level. BGP peers using MD5 authentication are configured with the same password. If the password authentication fails, then the packets are not transmitted along the segment.

Configuring BGP MD5 Authentication

You can use the configuration in this section to configure BGP MD5 authentication between two BGP peers.


Note


The configuration for MD5 authentication is identical on both peers.


Configuration

Use the following configuration to configure BGP MD5:

RP/0/RP0/CPU0:router(config)# router bgp 50
RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-af)# exit 
RP/0/RP0/CPU0:router(config-bgp)# neighbor 10.1.1.1 
RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 51
RP/0/RP0/CPU0:router(config-bgp-nbr)# password encrypted a1b2c3 
RP/0/RP0/CPU0:router(config-bgp-nbr)# commit 
Running Configuration

Validate the configuration.

RP/0/RP0/CPU0:router# show running-config
...
!
router bgp 50
address-family ipv4 unicast
!
neighbor 10.1.1.1
remote-as 51
password encrypted a1b2c3
!
!

Hiding the Local AS Number for BGP Networks

Changing the autonomous system number is necessary when two separate BGP networks are combined under a single autonomous system. The neighbor local-as command is used to configure BGP peers to support two local autonomous system numbers to maintain peering between two separate BGP networks.

However, when the neighbor local-as command is configured on a BGP peer, the local AS number is automatically prepended to all routes that are learned from eBGP peers by default. This behavior, however, makes changing the autonomous system number for a service provider or large BGP network difficult, because the routes with the prepended AS number are rejected by internal BGP (iBGP) peers that belong to the same AS.

Hiding the local AS number by using the no-prepend command simplifies the process of changing the autonomous system number in a Border Gateway Protocol (BGP) network. Without this feature, internal BGP (iBGP) peers reject external routes from peers with a local AS number in the as-path attribute to prevent routing loops. Hiding the local AS number allows you to transparently change the autonomous system number for the entire BGP network and ensure that routes can be propagated throughout the autonomous system, while the AS number transition is incomplete.

Configuring BGP to Hide the Local AS Number

Hiding the local AS number for eBGP peers by using the no-prepend command can be used to transparently change the AS number of a BGP network, and ensure that routes are propagated throughout the AS during the transition. Because the local AS number is not prepended to these routes, external routes are not rejected by internal peers during the transition from one AS number to another.

This section describes the configuration and verification of the feature.


Note


BGP prepends the autonomous system number from each BGP network that a route traverses. This behavior is designed to maintain network reachability information and to prevent routing loops from occurring. Configuring the no-prepend command incorrectly could create routing loops. So, the configuration of this command should only be attempted by an experienced network operator.


Configuration

Use the following configuration to hide the local AS number for eBGP peers.

Router# config
Router(config)# router bgp 100
Router(config-bgp)# address-family ipv4 unicast
Router(config-bgp-af)# network 172.20.1.1 255.255.240.0
Router(config-bgp-af)# neighbor 172.20.1.1
Router(config-bgp-af)# remote-as 150
Router(config-bgp-af)# local-as 300 no-prepend 
Router(config-bgp-af)# commit

Running Configuration
RP/0/RP0/CPU0:router# show running-configuration
...
!
router bgp 100
 address-family ipv4 unicast
 network 10.1.1.1 255.255.0.0
 neighbor 10.1.1.1 remote-as 100
 neighbor 10.1.1.1 local-as 300 no-prepend
!

Verification

Use the following command to verify your configuration.

RP/0/RP0/CPU0:router# show ip bgp neighbors
BGP neighbor is 10.1.1.1, remote AS 100, local AS 300 no-prepend, external link
BGP version 4, remote router ID 10.1.1.1
BGP state = Established, up for 00:00:49
Last read 00:00:49, hold time is 180, keepalive interval is 60 seconds
Neighbor capabilities:
Route refresh: advertised and received(new)
Address family IPv4 Unicast: advertised and received
IPv4 MPLS Label capability:
Received 10 messages, 1 notifications, 0 in queue
Sent 10 messages, 0 notifications, 0 in queue
Default minimum time between advertisement runs is 30 seconds

Autonomous System Number Formats in BGP

Autonomous system numbers (ASNs) are globally unique identifiers used to identify autonomous systems (ASs) and enable ASs to exchange exterior routing information between neighboring ASs. A unique ASN is allocated to each AS for use in BGP routing. ASNs are encoded as 2-byte numbers and 4-byte numbers in BGP.


RP/0/RP0/CPU0:router(config)# as-format [asdot | asplain]
RP/0/RP0/CPU0:router(config)# as-format asdot


Note


ASN change for BGP process is not currently supported via commit replace command.


2-byte Autonomous System Number Format

The 2-byte ASNs are represented in asplain notation. The 2-byte range is 1 to 65535.

4-byte Autonomous System Number Format

To prepare for the eventual exhaustion of 2-byte Autonomous System Numbers (ASNs), BGP has the capability to support 4-byte ASNs. The 4-byte ASNs are represented both in asplain and asdot notations.

The byte range for 4-byte ASNs in asplain notation is 1-4294967295. The AS is represented as a 4-byte decimal number. The 4-byte ASN asplain representation is defined in draft-ietf-idr-as-representation-01.txt.

For 4-byte ASNs in asdot format, the 4-byte range is 1.0 to 65535.65535 and the format is:

high-order-16-bit-value-in-decimal . low-order-16-bit-value-in-decimal

The BGP 4-byte ASN capability is used to propagate 4-byte-based AS path information across BGP speakers that do not support 4-byte AS numbers. See draft-ietf-idr-as4bytes-12.txt for information on increasing the size of an ASN from 2 bytes to 4 bytes. AS is represented as a 4-byte decimal number

as-format Command

The as-format command configures the ASN notation to asdot. The default value, if the as-format command is not configured, is asplain.

BGP Multi-Instance and Multi-AS

Multi-AS BGP enables configuring each instance of a multi-instance BGP with a different AS number. Multi-Instance and Multi-AS BGP provides these capabilities:
  • Mechanism to consolidate the services provided by multiple routers using a common routing infrastructure into a single IOS-XR router.

  • Mechanism to achieve AF isolation by configuring the different AFs in different BGP instances.

  • Means to achieve higher session scale by distributing the overall peering sessions between multiple instances.

  • Mechanism to achieve higher prefix scale (especially on a RR) by having different instances carrying different BGP tables.

  • Improved BGP convergence under certain scenarios.

  • All BGP functionalities including NSR are supported for all the instances.

  • The load and commit router-level operations can be performed on previously verified or applied configurations.

Restrictions
  • The router supports maximum of 4 BGP instances.

  • Each BGP instance needs a unique router-id.

  • Only one Address Family can be configured under each BGP instance (VPNv4, VPNv6 and RT-Constrain can be configured under multiple BGP instances).

  • IPv4/IPv6 Unicast should be within the same BGP instance in which IPv4/IPv6 Labeled-Unicast is configured.

  • IPv4/IPv6 Multicast should be within the same BGP instance in which IPv4/IPv6 Unicast is configured.

  • All configuration changes for a single BGP instance can be committed together. However, configuration changes for multiple instances cannot be committed together.

  • Cisco recommends that BGP update-source should be unique in the default VRF over all instances while peering with the same remote router.

Configure Multiple BGP Instances for a Specific Autonomous System

Perform this task to configure multiple BGP instances for a specific autonomous system. All configuration changes for a single BGP instance can be committed together. However, configuration changes for multiple instances cannot be committed together.

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number [instance instance name ]

Example:
RP/0/RSP0/CPU0:router(config)# router bgp 100 instance inst1

Enters BGP configuration mode for the user specified BGP instance.

Step 3

bgp router-id ip-address

Example:
RP/0/RSP0/CPU0:router(config-bgp)# bgp router-id 10.0.0.0

Configures a fixed router ID for the BGP-speaking router (BGP instance).

Note

 

You must manually configure unique router ID for each BGP instance.

Step 4

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


BGP Routing Domain Confederation

One way to reduce the iBGP mesh is to divide an autonomous system into multiple sub-autonomous systems and group them into a single confederation. To the outside world, the confederation looks like a single autonomous system. Each autonomous system is fully meshed within itself and has a few connections to other autonomous systems in the same confederation. Although the peers in different autonomous systems have eBGP sessions, they exchange routing information as if they were iBGP peers. Specifically, the next hop, MED, and local preference information is preserved. This feature allows you to retain a single IGP for all of the autonomous systems.

Configure Routing Domain Confederation for BGP

Perform this task to configure the routing domain confederation for BGP. This includes specifying a confederation identifier and autonomous systems that belong to the confederation.

Configuring a routing domain confederation reduces the internal BGP (iBGP) mesh by dividing an autonomous system into multiple autonomous systems and grouping them into a single confederation. Each autonomous system is fully meshed within itself and has a few connections to another autonomous system in the same confederation. The confederation maintains the next hop and local preference information, and that allows you to retain a single Interior Gateway Protocol (IGP) for all autonomous systems. To the outside world, the confederation looks like a single autonomous system.

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router# router bgp 120

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

bgp confederation identifier as-number

Example:

RP/0/RP0/CPU0:router(config-bgp)# bgp confederation identifier 5

Specifies a BGP confederation identifier.

Step 4

bgp confederation peers as-number

Example:

RP/0/RP0/CPU0:router(config-bgp)# bgp confederation peers 1091
  RP/0/RP0/CPU0:router(config-bgp)# bgp confederation peers 1092
  RP/0/RP0/CPU0:router(config-bgp)# bgp confederation peers 1093
  RP/0/RP0/CPU0:router(config-bgp)# bgp confederation peers 1094
  RP/0/RP0/CPU0:router(config-bgp)# bgp confederation peers 1095
  RP/0/RP0/CPU0:router(config-bgp)# bgp confederation peers 1096
  

Specifies that the BGP autonomous systems belong to a specified BGP confederation identifier. You can associate multiple AS numbers to the same confederation identifier, as shown in the example.

Step 5

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


BGP Confederation: Example

The following is a sample configuration that shows several peers in a confederation. The confederation consists of three internal autonomous systems with autonomous system numbers 6001, 6002, and 6003. To the BGP speakers outside the confederation, the confederation looks like a normal autonomous system with autonomous system number 666 (specified using the bgp confederation identifier command).

In a BGP speaker in autonomous system 6001, the bgp confederation peers command marks the peers from autonomous systems 6002 and 6003 as special eBGP peers. Hence, peers 171.16 .232.55 and 171.16 .232.56 get the local preference, next hop, and MED unmodified in the updates. The router at 171 .19 .69.1 is a normal eBGP speaker, and the updates received by it from this peer are just like a normal eBGP update from a peer in autonomous system 666.


  router bgp 6001
   bgp confederation identifier 666
   bgp confederation peers 
    6002
    6003
     exit
   address-family ipv4 unicast
    neighbor 171.16.232.55 
    remote-as 6002
     exit
   address-family ipv4 unicast
    neighbor 171.16.232.56 
    remote-as 6003
     exit
   address-family ipv4 unicast
    neighbor 171.19.69.1 
    remote-as 777
  
  
In a BGP speaker in autonomous system 6002, the peers from autonomous systems 6001 and 6003 are configured as special eBGP peers. Peer 171 .17 .70.1 is a normal iBGP peer, and peer 199.99.99.2 is a normal eBGP peer from autonomous system 700.

  router bgp 6002
   bgp confederation identifier 666
   bgp confederation peers 
    6001
    6003
     exit
   address-family ipv4 unicast
    neighbor 171.17.70.1 
     remote-as 6002
     exit
   address-family ipv4 unicast
    neighbor 171.19.232.57 
     remote-as 6001
     exit
   address-family ipv4 unicast
    neighbor 171.19.232.56 
     remote-as 6003
     exit
   address-family ipv4 unicast
    neighbor 171.19.99.2 
     remote-as 700
     exit
   address-family ipv4 unicast
    route-policy pass-all in
    route-policy pass-all out
  
  
In a BGP speaker in autonomous system 6003, the peers from autonomous systems 6001 and 6002 are configured as special eBGP peers. Peer 192 .168 .200.200 is a normal eBGP peer from autonomous system 701.

  router bgp 6003
   bgp confederation identifier 666
   bgp confederation peers
    6001
    6002
     exit
   address-family ipv4 unicast
    neighbor 171.19.232.57 
     remote-as 6001
     exit
   address-family ipv4 unicast
    neighbor 171.19.232.55 
     remote-as 6002
     exit
   address-family ipv4 unicast
    neighbor 192.168.200.200 
     remote-as 701
     exit
   address-family ipv4 unicast
    route-policy pass-all in
    route-policy pass-all out
  
  
The following is a part of the configuration from the BGP speaker 192 .168 .200.205 from autonomous system 701 in the same example. Neighbor 171.16 .232.56 is configured as a normal eBGP speaker from autonomous system 666. The internal division of the autonomous system into multiple autonomous systems is not known to the peers external to the confederation.

  router bgp 701
   address-family ipv4 unicast
    neighbor 172.16.232.56 
     remote-as 666
     exit
   address-family ipv4 unicast
    route-policy pass-all in
    route-policy pass-all out
     exit
   address-family ipv4 unicast
    neighbor 192.168.200.205 
     remote-as 701
  

BGP Additional Paths

The Border Gateway Protocol (BGP) Additional Paths feature modifies the BGP protocol machinery for a BGP speaker to be able to send multiple paths for a prefix. This gives 'path diversity' in the network. The add path enables BGP prefix independent convergence (PIC) at the edge routers.

BGP add path enables add path advertisement in an iBGP network and advertises the following types of paths for a prefix:

  • Backup paths—to enable fast convergence and connectivity restoration.

  • Group-best paths—to resolve route oscillation.

  • All paths—to emulate an iBGP full-mesh.

Configure BGP Additional Paths

Perform these tasks to configure BGP Additional Paths capability:

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

route-policy route-policy-name

Example:
RP/0/RP0/CPU0:router (config)#route-policy add_path_policy

Defines the route policy and enters route-policy configuration mode.

Step 3

if conditional-expression then action-statement else

Example:
RP/0/RP0/CPU0:router (config-rpl)#if community matches-any (*) then
    set path-selection all advertise
  else

Decides the actions and dispositions for the given route.

Step 4

pass endif

Example:

RP/0/RP0/CPU0:router(config-rpl-else)#pass
RP/0/RP0/CPU0:router(config-rpl-else)#endif

Passes the route for processing and ends the if statement.

Step 5

end-policy

Example:
RP/0/RP0/CPU0:router(config-rpl)#end-policy

Ends the route policy definition of the route policy and exits route-policy configuration mode.

Step 6

router bgp as-number

Example:
RP/0/RP0/CPU0:router(config)#router bgp 100

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 7

address-family {ipv4 {unicast } | ipv6 {unicast | l2vpn vpls-vpws | vpnv4 unicast | vpnv6 unicast }

Example:
RP/0/RP0/CPU0:router(config-bgp)#address-family ipv4 unicast

Specifies the address family and enters address family configuration submode.

Step 8

additional-paths receive

Example:
RP/0/RP0/CPU0:router(config-bgp-af)#additional-paths receive

Configures receive capability of multiple paths for a prefix to the capable peers.

Step 9

additional-paths send

Example:
RP/0/RP0/CPU0:router(config-bgp-af)#additional-paths send

Configures send capability of multiple paths for a prefix to the capable peers .

Step 10

additional-paths selection route-policy route-policy-name

Example:
RP/0/RP0/CPU0:router(config-bgp-af)#additional-paths selection route-policy add_path_policy

Configures additional paths selection capability for a prefix.

Step 11

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


BGP Maximum Prefix

The maximum-prefix feature imposes a maximum limit on the number of prefixes that are received from a neighbor for a given address family. Whenever the number of prefixes received exceeds the maximum number configured, the BGP session is terminated, which is the default behavior, after sending a cease notification to the neighbor. The session is down until a manual clear is performed by the user. The session can be resumed by using the clear bgp command. It is possible to configure a period after which the session can be automatically brought up by using the maximum-prefix command with the restart keyword. The maximum prefix limit can be configured by the user. Default limits are used if the user does not configure the maximum number of prefixes for the address family.

Discard Extra Paths

An option to discard extra paths is added to the maximum-prefix configuration. Configuring the discard extra paths option drops all excess prefixes received from the neighbor when the prefixes exceed the configured maximum value. This drop does not, however, result in session flap.

The benefits of discard extra paths option are:

  • Limits the memory footstamp of BGP.

  • Stops the flapping of the peer if the paths exceed the set limit.

When the discard extra paths configuration is removed, BGP sends a route-refresh message to the neighbor if it supports the refresh capability; otherwise the session is flapped.

On the same lines, the following describes the actions when the maximum prefix value is changed:

  • If the maximum value alone is changed, a route-refresh message is sourced, if applicable.

  • If the new maximum value is greater than the current prefix count state, the new prefix states are saved.

  • If the new maximum value is less than the current prefix count state, then some existing prefixes are deleted to match the new configured state value.

There is currently no way to control which prefixes are deleted.

Configure Discard Extra Paths

The discard extra paths option in the maximum-prefix configuration allows you to drop all excess prefixes received from the neighbor when the prefixes exceed the configured maximum value. This drop does not, however, result in session flap.

The benefits of discard extra paths option are:

  • Limits the memory footstamp of BGP.

  • Stops the flapping of the peer if the paths exceed the set limit.

When the discard extra paths configuration is removed, BGP sends a route-refresh message to the neighbor if it supports the refresh capability; otherwise the session is flapped.

Note


  • When the router drops prefixes, it is inconsistent with the rest of the network, resulting in possible routing loops.

  • If prefixes are dropped, the standby and active BGP sessions may drop different prefixes. Consequently, an NSR switchover results in inconsistent BGP tables.

  • The discard extra paths configuration cannot co-exist with the soft reconfig configuration.

  • When the system runs out of physical memory, bgp process exits and you must manually restart bpm. To manually restart, use the process restart bpm command.


Perform this task to configure BGP maximum-prefix discard extra paths.

Procedure

Step 1

configure

Example:
RP/0/RP0/CPU0:router# configure

Enters XR Config mode.

Step 2

router bgp as-number

Example:
RP/0/RP0/CPU0:router(config)# router bgp 10 

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

neighbor ip-address

Example:
RP/0/RP0/CPU0:router(config-bgp)# neighbor 10.0.0.1 

Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address as a BGP peer.

Step 4

address-family { ipv4 | ipv6 } unicast

Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family ipv4 unicast 

Specifies either the IPv4 or IPv6 address family and enters address family configuration submode.

Step 5

maximum-prefix maximum discard-extra-paths

Example:
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# maximum-prefix 1000 discard-extra-paths 

Configures a limit to the number of prefixes allowed.

Configures discard extra paths to discard extra paths when the maximum prefix limit is exceeded.

Step 6

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Example

The following example shows how to configure discard extra paths feature for the IPv4 address family:


RP/0/RP0/CPU0:router# configure
RP/0/RP0/CPU0:router(config)# router bgp 10
RP/0/RP0/CPU0:router(config-bgp)# neighbor 10.0.0.1
RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# maximum-prefix 1000 discard-extra-paths
RP/0/RP0/CPU0:router(config-bgp-vrf-af)# commit

The show bgp neighbor output shows the cumulative number for the Prefix advertised count if the same prefixes are withdrawn and re-advertised.

The following screen output shows details about the discard extra paths option:


RP/0/RP0/CPU0:ios# show bgp neighbor 10.0.0.1 

BGP neighbor is 10.0.0.1
Remote AS 10, local AS 10, internal link
Remote router ID 0.0.0.0
BGP state = Idle (No best local address found)
Last read 00:00:00, Last read before reset 00:00:00
Hold time is 180, keepalive interval is 60 seconds
Configured hold time: 180, keepalive: 60, min acceptable hold time: 3
Last write 00:00:00, attempted 0, written 0
Second last write 00:00:00, attempted 0, written 0
Last write before reset 00:00:00, attempted 0, written 0
Second last write before reset 00:00:00, attempted 0, written 0
Last write pulse rcvd not set last full not set pulse count 0
Last write pulse rcvd before reset 00:00:00
Socket not armed for io, not armed for read, not armed for write
Last write thread event before reset 00:00:00, second last 00:00:00
Last KA expiry before reset 00:00:00, second last 00:00:00
Last KA error before reset 00:00:00, KA not sent 00:00:00
Last KA start before reset 00:00:00, second last 00:00:00
Precedence: internet
Multi-protocol capability not received
Received 0 messages, 0 notifications, 0 in queue
Sent 0 messages, 0 notifications, 0 in queue
Minimum time between advertisement runs is 0 secs

For Address Family: IPv4 Unicast
BGP neighbor version 0
Update group: 0.1 Filter-group: 0.0 No Refresh request being processed
Route refresh request: received 0, sent 0
0 accepted prefixes, 0 are bestpaths
Cumulative no. of prefixes denied: 0. 
Prefix advertised 0, suppressed 0, withdrawn 0
Maximum prefixes allowed 10 (discard-extra-paths) <<<<<<<<<<<<<<<<<<<<<
Threshold for warning message 75%, restart interval 0 min
AIGP is enabled
An EoR was not received during read-only mode
Last ack version 1, Last synced ack version 0
Outstanding version objects: current 0, max 0
Additional-paths operation: None
Send Multicast Attributes

Connections established 0; dropped 0
Local host: 0.0.0.0, Local port: 0, IF Handle: 0x00000000
Foreign host: 10.0.0.1, Foreign port: 0
Last reset 00:00:00

BGP Best-External Path

The best–external path functionality supports advertisement of the best–external path to the iBGP and Route Reflector peers when a locally selected bestpath is from an internal peer. BGP selects one best path and one backup path to every destination. By default, selects one best path . Additionally, BGP selects another bestpath from among the remaining external paths for a prefix. Only a single path is chosen as the best–external path and is sent to other PEs as the backup path. BGP calculates the best–external path only when the best path is an iBGP path. If the best path is an eBGP path, then best–external path calculation is not required.

The procedure to determine the best–external path is as follows:

  1. Determine the best path from the entire set of paths available for a prefix.

  2. Eliminate the current best path.

  3. Eliminate all the internal paths for the prefix.

  4. From the remaining paths, eliminate all the paths that have the same next hop as that of the current best path.

  5. Rerun the best path algorithm on the remaining set of paths to determine the best–external path.

BGP considers the external and confederations BGP paths for a prefix to calculate the best–external path. BGP advertises the best path and the best–external path as follows:

  • On the primary PE—advertises the best path for a prefix to both its internal and external peers

  • On the backup PE—advertises the best path selected for a prefix to the external peers and advertises the best–external path selected for that prefix to the internal peers

Configure Best-External Path Advertisement

Perform the following tasks to advertise the best–external path to the iBGP and route-reflector peers:

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 100

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

Do one of the following

  • address-family { vpnv4 unicast | vpnv6 unicast }
  • vrf vrf-name { ipv4 unicast |ipv6 unicast }
Example:

RP/0/RP0/CPU0:router(config-bgp)# address-family vpnv4 unicast

Specifies the address family or VRF address family and enters the address family or VRF address family configuration submode.

Step 4

advertise best-external

Example:

RP/0/RP0/CPU0:router(config-bgp-af)# advertise best-external

Advertise the best–external path to the iBGP and route-reflector peers.

Step 5

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


BGP Local Label Retention

When a primary PE-CE link fails, BGP withdraws the route corresponding to the primary path along with its local label and programs the backup path in the Routing Information Base (RIB) and the Forwarding Information Base (FIB), by default.

However, until all the internal peers of the primary PE reconverge to use the backup path as the new bestpath, the traffic continues to be forwarded to the primary PE with the local label that was allocated for the primary path. Hence the previously allocated local label for the primary path must be retained on the primary PE for some configurable time after the reconvergence. BGP Local Label Retention feature enables the retention of the local label for a specified period. If no time is specified, the local lable is retained for a default value of five minutes.

Retain Allocated Local Label for Primary Path

Perform the following tasks to retain the previously allocated local label for the primary path on the primary PE for some configurable time after reconvergence:

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 100

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

address-family { vpnv4 unicast | vpnv6 unicast }

Example:

RP/0/RP0/CPU0:router(config-bgp)# address-family vpnv4 unicast

Specifies the address family and enters the address family configuration submode.

Step 4

retain local-label minutes

Example:

RP/0/RP0/CPU0:router(config-bgp-af)# retain local-label 10

Retains the previously allocated local label for the primary path on the primary PE for 10 minutes after reconvergence.

Step 5

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Allocated Local Label Retention: Example

The following example shows how to retain the previously allocated local label for the primary path on the primary PE for 10 minutes after reconvergence:


  router bgp 100
  address-family l2vpn vpnv4 unicast
    retain local-label 10
  end
  

iBGP Multipath Load Sharing

When a Border Gateway Protocol (BGP) speaking router that has no local policy configured, receives multiple network layer reachability information (NLRI) from the internal BGP (iBGP) for the same destination, the router will choose one iBGP path as the best path. The best path is then installed in the IP routing table of the router. The iBGP Multipath Load Sharing feature enables the BGP speaking router to select multiple iBGP paths as the best paths to a destination. The best paths or multipaths are then installed in the IP routing table of the router.

iBGP Multipath Load Sharing Reference provides additional details.

Configure iBGP Multipath Load Sharing

Perform this task to configure the iBGP Multipath Load Sharing:

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:
RP/0/RP0/CPU0:router(config)# router bgp 100

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

address-family {ipv4 |ipv6 } {unicast |multicast }

Example:
RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 multicast

Specifies either the IPv4 or IPv6 address family and enters address family configuration submode.

Step 4

maximum-paths ibgp number

Example:
RP/0/RP0/CPU0:router(config-bgp-af)# maximum-paths ibgp 30

Configures the maximum number of iBGP paths for load sharing.

Step 5

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


iBGP Multipath Loadsharing Configuration: Example

The following is a sample configuration where 30 paths are used for loadsharing:


router bgp 100
 address-family ipv4 multicast
  maximum-paths ibgp 30
 !
!
end

Persistent Loadbalancing

Traditional ECMP or equal cost multipath loadbalances traffic over a number of available paths towards a destination. When one path fails, the traffic gets re-shuffled over the available number of paths. This flow distribution can be a problem in data center loadbalancing.

Persistent Loadbalancing or Sticky ECMP defines a prefix in such a way that it do not rehash flows on existing paths and only replace those bucket assignments of the failed server. The advantage is that the established sessions to servers will not get rehashed.

The following section describes how you can configure persistent load balancing:

/*Configure persistent load balancing. */

Router(config)# router bgp 7500 
Router(config-bgp)# address-family ipv4 unicast 
Router(config-bgp-af)# table-policy sticky-ecmp 
Router(config-bgp-af)# bgp attribute-download 
Router(config-bgp-af)# maximum-paths ebgp 64
Router(config-bgp-af)# maximum-paths ibgp 32
Router(config-bgp-af)# exit
Router(config-bgp)# exit
Router(config)# route-policy sticky-ecmp 
Router(config-rpl)# if destination in (192.1.1.1/24) then
Router(config-rpl-if)# set load-balance ecmp-consistent
Router(config-rpl-if)# else
Router(config-rpl-else)# pass
Router(config-rpl-else)# endif
RP/0/0/CPU0:ios(config-rpl)# end-policy
RP/0/0/CPU0:ios(config)#

/* Enable autocovery and hence recover the original hashing state 
after failed paths become active. */
Router(config)# cef consistent-hashing auto-recovery

/* Recover to the original hashing state after failed paths come up 
and avoid affecting newly formed flows after path failure.  */
Router(config)# clear route 192.0.2.0/24 

Running Configuration

/* Configure persistent loadbalancing. */
router bgp 7500 
 address-family ipv4 unicast 
  table-policy sticky-ecmp 
  bgp attribute-download 
  maximum-paths ebgp 64
  maximum-paths ibgp 32


cef consistent-hashing auto-recovery

clear route 192.0.2.0/24 

Verification

Verify that the path distribution with persistent loadbalancing is configured.

The following show output displays the status of path distribution before a link fails. In this output, three paths are identified with three next hops (10.1/2/3.0.1) through three different GigabitEthernet interfaces.

 
show cef 192.0.2.0/24 
 LDI Update time Sep  5 11:22:38.201
   via 10.1.0.1/32, 3 dependencies, recursive, bgp-multipath [flags 0x6080]
    path-idx 0 NHID 0x0 [0x57ac4e74 0x0]
    next hop 10.1.0.1/32 via 10.1.0.1/32
   via 10.2.0.1/32, 3 dependencies, recursive, bgp-multipath [flags 0x6080]
    path-idx 1 NHID 0x0 [0x57ac4a74 0x0]
    next hop 10.2.0.1/32 via 10.2.0.1/32
   via 10.3.0.1/32, 3 dependencies, recursive, bgp-multipath [flags 0x6080]
    path-idx 2 NHID 0x0 [0x57ac4f74 0x0]
    next hop 10.3.0.1/32 via 10.3.0.1/32


    Load distribution (consistent): 0 1 2 (refcount 1)

    Hash  OK  Interface                 Address
    0     Y   GigabitEthernet0/0/0/0    10.1.0.1       
    1     Y   GigabitEthernet0/0/0/1    10.2.0.1       
    2     Y   GigabitEthernet0/0/0/2    10.3.0.1    

The following show output displays the status of the path distribution after a link fails. The replacement of bucket 1 with GigabitEthernet 0/0/0/0 and the "*" symbol denotes that this path is a replacement for a failed path.



show cef 192.0.2.0/24 
 LDI Update time Sep  5 11:23:13.434
   via 10.1.0.1/32, 3 dependencies, recursive, bgp-multipath [flags 0x6080]
    path-idx 0 NHID 0x0 [0x57ac4e74 0x0]
    next hop 10.1.0.1/32 via 10.1.0.1/32
   via 10.3.0.1/32, 3 dependencies, recursive, bgp-multipath [flags 0x6080]
    path-idx 1 NHID 0x0 [0x57ac4f74 0x0]
    next hop 10.3.0.1/32 via 10.3.0.1/32

    Load distribution (consistent) : 0 1 2 (refcount 1)
    Hash  OK  Interface                 Address
    0     Y   GigabitEthernet0/0/0/0    10.1.0.1       
 1*    Y   GigabitEthernet0/0/0/0    10.1.0.1       
    2     Y   GigabitEthernet0/0/0/2    10.3.0.1     

Route Dampening

Route dampening is a BGP feature that minimizes the propagation of flapping routes across an internetwork. A route is considered to be flapping when it is repeatedly available, then unavailable, then available, then unavailable, and so on.

For example, consider a network with three BGP autonomous systems: autonomous system 1, autonomous system 2, and autonomous system 3. Suppose the route to network A in autonomous system 1 flaps (it becomes unavailable). Under circumstances without route dampening, the eBGP neighbor of autonomous system 1 to autonomous system 2 sends a withdraw message to autonomous system 2. The border router in autonomous system 2, in turn, propagates the withdrawal message to autonomous system 3. When the route to network A reappears, autonomous system 1 sends an advertisement message to autonomous system 2, which sends it to autonomous system 3. If the route to network A repeatedly becomes unavailable, then available, many withdrawal and advertisement messages are sent. Route flapping is a problem in an internetwork connected to the Internet, because a route flap in the Internet backbone usually involves many routes.

The route dampening feature minimizes the flapping problem as follows. Suppose again that the route to network A flaps. The router in autonomous system 2 (in which route dampening is enabled) assigns network A a penalty of 1000 and moves it to history state. The router in autonomous system 2 continues to advertise the status of the route to neighbors. The penalties are cumulative. When the route flaps so often that the penalty exceeds a configurable suppression limit, the router stops advertising the route to network A, regardless of how many times it flaps. Thus, the route is dampened.

The penalty placed on network A is decayed until the reuse limit is reached, upon which the route is once again advertised. At half of the reuse limit, the dampening information for the route to network A is removed.


Note


No penalty is applied to a BGP peer reset when route dampening is enabled, even though the reset withdraws the route.


Configuring BGP Route Dampening

Perform this task to configure and monitor BGP route dampening.

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

address-family { ipv4 | ipv6 } unicast

Example:

RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 unicast

Specifies either the IPv4 or IPv6 address family and enters address family configuration submode.

To see a list of all the possible keywords and arguments for this command, use the CLI help (?).

Step 4

bgp dampening [ half-life [ reuse suppress max-suppress-time ] | route-policy route-policy-name ]

Example:

RP/0/RP0/CPU0:router(config-bgp-af)# bgp dampening 30 1500 10000 120

Configures BGP dampening for the specified address family.

Step 5

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Routing Policy Enforcement

External BGP (eBGP) neighbors must have an inbound and outbound policy configured. If no policy is configured, no routes are accepted from the neighbor, nor are any routes advertised to it. This added security measure ensures that routes cannot accidentally be accepted or advertised in the case of a configuration omission error.


Note


This enforcement affects only eBGP neighbors (neighbors in a different autonomous system than this router). For internal BGP (iBGP) neighbors (neighbors in the same autonomous system), all routes are accepted or advertised if there is no policy.


Apply Policy When Updating Routing Table

The table policy feature in BGP allows you to configure traffic index values on routes as they are installed in the global routing table. This feature is enabled using the table-policy command and supports the BGP policy accounting feature. Table policy also provides the ability to drop routes from the RIB based on match criteria. This feature can be useful in certain applications and should be used with caution as it can easily create a routing traffic drop where BGP advertises routes to neighbors that BGP does not install in its global routing table and forwarding table.

Perform this task to apply a routing policy to routes being installed into the routing table.

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 120.6

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

address-family { ipv4 | ipv6 } unicast

Example:

RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 unicast

Specifies either the IPv4 or IPv6 address family and enters address family configuration submode.

To see a list of all the possible keywords and arguments for this command, use the CLI help (?).

Step 4

table-policy policy-name

Example:

RP/0/RP0/CPU0:router(config-bgp-af)# table-policy tbl-plcy-A

Applies the specified policy to routes being installed into the routing table.

Step 5

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Applying routing policy: Example

In the following example, for an eBGP neighbor, if all routes should be accepted and advertised with no modifications, a simple pass-all policy is configured:


  RP/0/RP0/CPU0:router(config)# route-policy pass-all
  RP/0/RP0/CPU0:router(config-rpl)# pass
  RP/0/RP0/CPU0:router(config-rpl)# end-policy
  RP/0/RP0/CPU0:router(config)# commit
  

Use the route-policy (BGP) command in the neighbor address-family configuration mode to apply the pass-all policy to a neighbor. The following example shows how to allow all IPv4 unicast routes to be received from neighbor 192.168.40.42 and advertise all IPv4 unicast routes back to it:


  RP/0/RP0/CPU0:router(config)# router bgp 1
  RP/0/RP0/CPU0:router(config-bgp)# neighbor 192.168.40.24
  RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 21
  RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family ipv4 unicast
  RP/0/RP0/CPU0:router(config-bgp-nbr-af)# route-policy pass-all in
  RP/0/RP0/CPU0:router(config-bgp-nbr-af)# route-policy pass-all out
  RP/0/RP0/CPU0:router(config-bgp-nbr-af)# commit
 

Use the show bgp summary command to display eBGP neighbors that do not have both an inbound and outbound policy for every active address family. In the following example, such eBGP neighbors are indicated in the output with an exclamation (!) mark:


  RP/0/RP0/CPU0:routershow bgp all all summary
  
  Address Family: IPv4 Unicast
  ============================
  
  BGP router identifier 10.0.0.1, local AS number 1
  BGP generic scan interval 60 secs
  BGP main routing table version 41
  BGP scan interval 60 secs
  BGP is operating in STANDALONE mode.
  
  Process         RecvTblVer    bRIB/RIB  SendTblVer
  Speaker                 41          41          41
  
  Neighbor        Spk    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  St/PfxRcd
  10.0.101.1        0     1     919     925       41    0    0 15:15:08       10
  10.0.101.2        0     2       0       0        0    0    0 00:00:00 Idle
  

Configure BGP Neighbor Group and Neighbors

Perform this task to configure BGP neighbor groups and apply the neighbor group configuration to a neighbor. A neighbor group is a template that holds address family-independent and address family-dependent configurations that are associated with the neighbor.

After a neighbor group is configured, each neighbor can inherit the configuration through the usecommand. If a neighbor is configured to use a neighbor group, the neighbor (by default) inherits the entire configuration of the neighbor group, which includes the address family-independent and address family-dependent configurations. The inherited configuration can be overridden if you directly configure commands for the neighbor or configure session groups or address family groups through the usecommand.

You can configure an address family-independent configuration under the neighbor group. An address family-dependent configuration requires you to configure the address family under the neighbor group to enter address family submode. From neighbor group configuration mode, you can configure address family-independent parameters for the neighbor group. Use the address-familycommand when in the neighbor group configuration mode. After specifying the neighbor group name using the neighbor group command, you can assign options to the neighbor group.


Note


All commands that can be configured under a specified neighbor group can be configured under a neighbor.



Note


In Cisco IOS-XR versions prior to 6.3.2, you cannot remove a autonomous system that belongs to a BGP neighbor and move it under a BGP neigbhorgroup using a single IOS-XR commit. Effective with 6.3.2, you can move the autonoums system from a neighbor to a neighbor group in a single IOS-XR commit.


Procedure


Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:


RP/0/RP0/CPU0:router(config)# router bgp 120 

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

address-family { ipv4 | ipv6 } unicast

Example:


RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 unicast

Specifies either an IPv4 or IPv6 address family unicast and enters address family configuration submode.

To see a list of all the possible keywords and arguments for this command, use the CLI help (?).

Step 4

exit

Example:


RP/0/RP0/CPU0:router(config-bgp-af)# exit

Exits the current configuration mode.

Step 5

neighbor-group name

Example:


RP/0/RP0/CPU0:router(config-bgp)# neighbor-group nbr-grp-A

Places the router in neighbor group configuration mode.

Step 6

remote-as as-number

Example:


RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# remote-as 2002

Creates a neighbor and assigns a remote autonomous system number to it.

Step 7

address-family { ipv4 | ipv6 } unicast

Example:


RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# address-family ipv4 unicast

Specifies either an IPv4 or IPv6 address family unicast and enters address family configuration submode.

To see a list of all the possible keywords and arguments for this command, use the CLI help (?).

Step 8

route-policy route-policy-name { in | out }

Example:


RP/0/RP0/CPU0:router(config-bgp-nbrgrp-af)# route-policy drop-as-1234 in

(Optional) Applies the specified policy to inbound IPv4 unicast routes.

Step 9

exit

Example:


RP/0/RP0/CPU0:router(config-bgp-nbrgrp-af)# exit

Exits the current configuration mode.

Step 10

exit

Example:


RP/0/RP0/CPU0:router(config-bgp-nbrgrp)# exit

Exits the current configuration mode.

Step 11

neighbor ip-address

Example:


RP/0/RP0/CPU0:router(config-bgp)# neighbor 172.168.40.24

Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address as a BGP peer.

Step 12

use neighbor-group group-name

Example:


RP/0/RP0/CPU0:router(config-bgp-nbr)# use neighbor-group nbr-grp-A

(Optional) Specifies that the BGP neighbor inherit configuration from the specified neighbor group.

Step 13

remote-as as-number

Example:


RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 2002

Creates a neighbor and assigns a remote autonomous system number to it.

Step 14

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


BGP Neighbor Configuration: Example

The following example shows how BGP neighbors on an autonomous system are configured to share information. In the example, a BGP router is assigned to autonomous system 109, and two networks are listed as originating in the autonomous system. Then the addresses of three remote routers (and their autonomous systems) are listed. The router being configured shares information about networks 172 .16 .0.0 and 192.168 .7.0 with the neighbor routers. The first router listed is in a different autonomous system; the second neighbor and remote-as commands specify an internal neighbor (with the same autonomous system number) at address 172 .26 .234.2; and the third neighbor and remote-as commands specify a neighbor on a different autonomous system.


  route-policy pass-all 
   pass
  end-policy
  router bgp 109
   address-family ipv4 unicast
    network 172.16.0.0 255.255.0.0
    network 192.168.7.0 255.255.0.0
    neighbor 172.16.200.1 
     remote-as 167

   address-family ipv4 unicast
    route-policy pass-all in
    route-policy pass-out out
    neighbor 172.26.234.2 
     remote-as 109

   address-family ipv4 unicast
    neighbor 172.26.64.19 
     remote-as 99

   address-family ipv4 unicast
    route-policy pass-all in
    route-policy pass-all out
  

Disable BGP Neighbor

Perform this task to administratively shut down a neighbor session without removing the configuration.

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 127

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

neighbor ip-address

Example:

RP/0/RP0/CPU0:router(config-bgp)# neighbor 172.168.40.24

Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address as a BGP peer.

Step 4

shutdown

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# shutdown

Disables all active sessions for the specified neighbor.

Step 5

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Resetting Neighbors Using BGP Inbound Soft Reset

Perform this task to trigger an inbound soft reset of the specified address families for the specified group or neighbors. The group is specified by the * , ip-address , as-number , or external keywords and arguments.

Resetting neighbors is useful if you change the inbound policy for the neighbors or any other configuration that affects the sending or receiving of routing updates. If an inbound soft reset is triggered, BGP sends a REFRESH request to the neighbor if the neighbor has advertised the ROUTE_REFRESH capability. To determine whether the neighbor has advertised the ROUTE_REFRESH capability, use the show bgp neighbors command.

Procedure
  Command or Action Purpose

Step 1

show bgp neighbors

Example:

RP/0/RP0/CPU0:router# show bgp neighbors

Verifies that received route refresh capability from the neighbor is enabled.

Step 2

soft  [ in [ prefix-filter ] | out ]

Example:

RP/0/RP0/CPU0:router# clear bgp ipv4 unicast 10.0.0.1 soft in

Soft resets a BGP neighbor.

  • The * keyword resets all BGP neighbors.

  • The ip-address argument specifies the address of the neighbor to be reset.

  • The as-number argument specifies that all neighbors that match the autonomous system number be reset.

  • The external keyword specifies that all external neighbors are reset.

Resetting Neighbors Using BGP Outbound Soft Reset

Perform this task to trigger an outbound soft reset of the specified address families for the specified group or neighbors. The group is specified by the * , ip-address , as-number , or external keywords and arguments.

Resetting neighbors is useful if you change the outbound policy for the neighbors or any other configuration that affects the sending or receiving of routing updates.

If an outbound soft reset is triggered, BGP resends all routes for the address family to the given neighbors.

To determine whether the neighbor has advertised the ROUTE_REFRESH capability, use the show bgp neighbors command.

Procedure
  Command or Action Purpose

Step 1

show bgp neighbors

Example:

RP/0/RP0/CPU0:router# show bgp neighbors

Verifies that received route refresh capability from the neighbor is enabled.

Step 2

Example:

RP/0/RP0/CPU0:router# clear bgp ipv4 unicast 10.0.0.2 soft out

Soft resets a BGP neighbor.

  • The * keyword resets all BGP neighbors.

  • The ip-address argument specifies the address of the neighbor to be reset.

  • The as-number argument specifies that all neighbors that match the autonomous system number be reset.

  • The external keyword specifies that all external neighbors are reset.

Reset Neighbors Using BGP Hard Reset

Perform this task to reset neighbors using a hard reset. A hard reset removes the TCP connection to the neighbor, removes all routes received from the neighbor from the BGP table, and then re-establishes the session with the neighbor. If the graceful keyword is specified, the routes from the neighbor are not removed from the BGP table immediately, but are marked as stale. After the session is re-established, any stale route that has not been received again from the neighbor is removed.

Procedure

clear bgp { ipv4 { unicast | labeled-unicast | all | tunnel tunnel | mdt } | ipv6 unicast | all | labeled-unicast } | all { unicast | multicast | all | labeled-unicast | mdt | tunnel } | vpnv4 unicast | vrf { vrf-name | all } { ipv4 unicast | labeled-unicast } | ipv6 unicast } | vpnv6 unicast } { * | ip-address | as as-number | external } [ graceful ] soft  [ in [ prefix-filter ] | out ] clear bgp { ipv4 | ipv6} { unicast | labeled-unicast }

Example:

RP/0/RP0/CPU0:router# clear bgp ipv4 unicast 10.0.0.3 long-lived-stale

Clears a BGP neighbor.

  • The * keyword resets all BGP neighbors.

  • The ip-address argument specifies the address of the neighbor to be reset.

  • The as-number argument specifies that all neighbors that match the autonomous system number be reset.

  • The external keyword specifies that all external neighbors are reset.

The graceful keyword specifies a graceful restart.


Configure Software to Store Updates from Neighbor

Perform this task to configure the software to store updates received from a neighbor.

The soft-reconfiguration inbound command causes a route refresh request to be sent to the neighbor if the neighbor is route refresh capable. If the neighbor is not route refresh capable, the neighbor must be reset to relearn received routes using the clear bgp soft command.


Note


Storing updates from a neighbor works only if either the neighbor is route refresh capable or the soft-reconfiguration inbound command is configured. Even if the neighbor is route refresh capable and the soft-reconfiguration inbound command is configured, the original routes are not stored unless the always option is used with the command. The original routes can be easily retrieved with a route refresh request. Route refresh sends a request to the peer to resend its routing information. The soft-reconfiguration inbound command stores all paths received from the peer in an unmodified form and refers to these stored paths during the clear. Soft reconfiguration is memory intensive.


Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 120 

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

neighbor ip-address

Example:

RP/0/RP0/CPU0:router(config-bgp)# neighbor 172.168.40.24

Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address as a BGP peer.

Step 4

address-family { ipv4 | ipv6 } unicast

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family ipv4 unicast

Specifies either an IPv4 or IPv6 address family unicast and enters address family configuration submode.

To see a list of all the possible keywords and arguments for this command, use the CLI help (?).

Step 5

soft-reconfiguration inbound [ always]

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr-af)# soft-reconfiguration inbound always

Configures the software to store updates received from a specified neighbor. Soft reconfiguration inbound causes the software to store the original unmodified route in addition to a route that is modified or filtered. This allows a “soft clear” to be performed after the inbound policy is changed.

Soft reconfiguration enables the software to store the incoming updates before apply policy if route refresh is not supported by the peer (otherwise a copy of the update is not stored). The always keyword forces the software to store a copy even when route refresh is supported by the peer.

Step 6

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Log Neighbor Changes

Logging neighbor changes is enabled by default. Use thebgp log neighbor changes disable command to turn off logging. Use the no bgp log neighbor changes disable command to turn logging back on, if it has been disabled.


RP/0/RP0/CPU0:(config)# router bgp 100
RP/0/RP0/CPU0:(config-bgp)# bgp log neighbor changes disable

RP/0/RP0/CPU0:(config)# router bgp 100
RP/0/RP0/CPU0:(config-bgp)# no bgp log neighbor changes disable

BGP Route Reflectors

BGP requires that all iBGP speakers be fully meshed. However, this requirement does not scale well when there are many iBGP speakers. Instead of configuring a confederation, you can reduce the iBGP mesh by using a route reflector configuration. With route reflectors, all iBGP speakers need not be fully meshed because there is a method to pass learned routes to neighbors. In this model, an iBGP peer is configured to be a route reflector responsible for passing iBGP learned routes to a set of iBGP neighbors.

In #concept_3069A67F47124831B884817915F11DF3__ , Router B is configured as a route reflector. When the route reflector receives routes advertised from Router A, it advertises them to Router C, and vice versa. This scheme eliminates the need for the iBGP session between routers A and C.

See BGP Route Reflectors Reference for additional details on route reflectors.

Configure Route Reflector for BGP

Perform this task to configure a route reflector for BGP.

All the neighbors configured with the route-reflector-clientcommand are members of the client group, and the remaining iBGP peers are members of the nonclient group for the local route reflector.

Together, a route reflector and its clients form a cluster. A cluster of clients usually has a single route reflector. In such instances, the cluster is identified by the software as the router ID of the route reflector. To increase redundancy and avoid a single point of failure in the network, a cluster can have more than one route reflector. If it does, all route reflectors in the cluster must be configured with the same 4-byte cluster ID so that a route reflector can recognize updates from route reflectors in the same cluster. The bgp cluster-id command is used to configure the cluster ID when the cluster has more than one route reflector.

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

bgp cluster-id cluster-id

Example:

RP/0/RP0/CPU0:router(config-bgp)# bgp cluster-id 192.168.70.1

Configures the local router as one of the route reflectors serving the cluster. It is configured with a specified cluster ID to identify the cluster.

Step 4

neighbor ip-address

Example:

  RP/0/RP0/CPU0:router(config-bgp)# neighbor 172.168.40.24
  

Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address as a BGP peer.

Step 5

remote-as as-number

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 2003

Creates a neighbor and assigns a remote autonomous system number to it.

Step 6

address-family { ipv4 | ipv6 } unicast

Example:

RP/0/RP0/CPU0:router(config-nbr)# address-family ipv4 unicast

Specifies either an IPv4 or IPv6 address family unicast and enters address family configuration submode.

To see a list of all the possible keywords and arguments for this command, use the CLI help (?).

Step 7

route-reflector-client

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr-af)# route-reflector-client

Configures the router as a BGP route reflector and configures the neighbor as its client.

Step 8

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


BGP Route Reflector: Example

The following example shows how to use an address family to configure internal BGP peer 10.1.1.1 as a route reflector client for unicast prefixes:


  router bgp 140
   address-family ipv4 unicast
    neighbor 10.1.1.1
     remote-as 140
     address-family ipv4 unicast
      route-reflector-client
      exit
  

Configure BGP Route Filtering by Route Policy

Perform this task to configure BGP routing filtering by route policy.

Procedure

  Command or Action Purpose

Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

route-policy name

Example:


RP/0/RP0/CPU0:router(config)# route-policy drop-as-1234
  RP/0/RP0/CPU0:router(config-rpl)# if as-path passes-through '1234' then
  RP/0/RP0/CPU0:router(config-rpl)# apply check-communities
  RP/0/RP0/CPU0:router(config-rpl)# else
  RP/0/RP0/CPU0:router(config-rpl)# pass
  RP/0/RP0/CPU0:router(config-rpl)# endif
  

(Optional) Creates a route policy and enters route policy configuration mode, where you can define the route policy.

Step 3

end-policy

Example:


RP/0/RP0/CPU0:router(config-rpl)# end-policy

(Optional) Ends the definition of a route policy and exits route policy configuration mode.

Step 4

router bgp as-number

Example:


RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 5

neighbor ip-address

Example:


RP/0/RP0/CPU0:router(config-bgp)# neighbor 172.168.40.24

Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address as a BGP peer.

Step 6

address-family { ipv4 | ipv6 } unicast

Example:


RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family ipv4 unicast

Specifies either an IPv4 or IPv6 address family unicast and enters address family configuration submode.

To see a list of all the possible keywords and arguments for this command, use the CLI help (?).

Step 7

route-policy route-policy-name { in | out }

Example:


RP/0/RP0/CPU0:router(config-bgp-nbr-af)# route-policy drop-as-1234 in

Applies the specified policy to inbound routes.

Step 8

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.

Configure BGP Attribute Filtering

The BGP Attribute Filter checks integrity of BGP updates in BGP update messages and optimizes reaction when detecting invalid attributes. BGP Update message contains a list of mandatory and optional attributes. These attributes in the update message include MED, LOCAL_PREF, COMMUNITY, and so on. In some cases, if the attributes are malformed, there is a need to filter these attributes at the receiving end of the router. The BGP Attribute Filter functionality filters the attributes received in the incoming update message. The attribute filter can also be used to filter any attributes that may potentially cause undesirable behavior on the receiving router. Some of the BGP updates are malformed due to wrong formatting of attributes such as the network layer reachability information (NLRI) or other fields in the update message. These malformed updates, when received, causes undesirable behavior on the receiving routers. Such undesirable behavior may be encountered during update message parsing or during re-advertisement of received NLRIs. In such scenarios, its better to filter these corrupted attributes at the receiving end.

The Attribute-filtering is configured by specifying a single or a range of attribute codes and an associated action. When a received Update message contains one or more filtered attributes, the configured action is applied on the message. Optionally, the Update message is also stored to facilitate further debugging and a syslog message is generated on the console. When an attribute matches the filter, further processing of the attribute is stopped and the corresponding action is taken. Perform the following tasks to configure BGP attribute filtering:

Procedure


Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:


RP/0/RP0/CPU0:router(config)# router bgp 100

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

attribute-filter group attribute-filter group name

Example:


RP/0/RP0/CPU0:router(config-bgp)# attribute-filter group ag_discard_med

Specifies the attribute-filter group name and enters the attribute-filter group configuration mode, allowing you to configure a specific attribute filter group for a BGP neighbor.

Step 4

attribute attribute code { discard | treat-as-withdraw }

Example:


RP/0/RP0/CPU0:router(config-bgp-attrfg)# attribute 24 discard
Specifies a single or a range of attribute codes and an associated action. The allowed actions are:
  • Treat-as-withdraw— Considers the update message for withdrawal. The associated IPv4-unicast or MP_REACH NLRIs, if present, are withdrawn from the neighbor's Adj-RIB-In.

  • Discard Attribute— Discards this attribute. The matching attributes alone are discarded and the rest of the Update message is processed normally.


BGP Next Hop Tracking

BGP receives notifications from the Routing Information Base (RIB) when next-hop information changes (event-driven notifications). BGP obtains next-hop information from the RIB to:

  • Determine whether a next hop is reachable.

  • Find the fully recursed IGP metric to the next hop (used in the best-path calculation).

  • Validate the received next hops.

  • Calculate the outgoing next hops.

  • Verify the reachability and connectedness of neighbors.

BGP Next Hop Reference provides additional conceptual details on BGP next hop.

Configure BGP Next-Hop Trigger Delay

Perform this task to configure BGP next-hop trigger delay. The Routing Information Base (RIB) classifies the dampening notifications based on the severity of the changes. Event notifications are classified as critical and noncritical. This task allows you to specify the minimum batching interval for the critical and noncritical events.

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

address-family { ipv4 | ipv6 } unicast

Example:

RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 unicast

Specifies either an IPv4 or IPv6 address family unicast and enters address family configuration submode.

To see a list of all the possible keywords and arguments for this command, use the CLI help (?).

Step 4

nexthop trigger-delay { critical delay | non-critical delay }

Example:

RP/0/RP0/CPU0:router(config-bgp-af)# nexthop trigger-delay critical 15000

Sets the critical next-hop trigger delay.

Step 5

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Disable Next-Hop Processing on BGP Updates

Perform this task to disable next-hop calculation for a neighbor and insert your own address in the next-hop field of BGP updates. Disabling the calculation of the best next hop to use when advertising a route causes all routes to be advertised with the network device as the next hop.


Note


Next-hop processing can be disabled for address family group, neighbor group, or neighbor address family.


Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

neighbor ip-address

Example:

RP/0/RP0/CPU0:router(config-bgp)# neighbor 172.168.40.24

Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address as a BGP peer.

Step 4

remote-as as-number

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 206

Creates a neighbor and assigns a remote autonomous system number to it.

Step 5

address-family { ipv4 | ipv6 } unicast

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family ipv4 unicast

Specifies either an IPv4 or IPv6 address family unicast and enters address family configuration submode.

To see a list of all the possible keywords and arguments for this command, use the CLI help (?).

Step 6

next-hop-self

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr-af)# next-hop-self

Sets the next-hop attribute for all routes advertised to the specified neighbor to the address of the local router. Disabling the calculation of the best next hop to use when advertising a route causes all routes to be advertised with the local network device as the next hop.

Step 7

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


BGP Cost Community

The BGP cost community is a nontransitive extended community attribute that is passed to internal BGP (iBGP) and confederation peers but not to external BGP (eBGP) peers. The cost community feature allows you to customize the local route preference and influence the best-path selection process by assigning cost values to specific routes. The extended community format defines generic points of insertion (POI) that influence the best-path decision at different points in the best-path algorithm.

BGP Cost Community Reference provides additional conceptual details on BGP cost community.

Configure BGP Cost Community

BGP receives multiple paths to the same destination and it uses the best-path algorithm to decide which is the best path to install in RIB. To enable users to determine an exit point after partial comparison, the cost community is defined to tie-break equal paths during the best-path selection process. Perform this task to configure the BGP cost community.

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

route-policy name

Example:

RP/0/RP0/CPU0:router(config)# route-policy costA

Enters route policy configuration mode and specifies the name of the route policy to be configured.

Step 3

set extcommunity cost { cost-extcommunity-set-name | cost-inline-extcommunity-set } [ additive ]

Example:

RP/0/RP0/CPU0:router(config)# set extcommunity cost cost_A

Specifies the BGP extended community attribute for cost.

Step 4

end-policy

Example:

RP/0/RP0/CPU0:router(config)# end-policy

Ends the definition of a route policy and exits route policy configuration mode.

Step 5

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 120

Enters BGP configuration mode allowing you to configure the BGP routing process.

Step 6

Do one of the following:

  • default-information originate
  • aggregate-address address/mask-length [ as-set ] [ as-confed-set ] [ summary-only ] [ route-policy route-policy-name ]
  • redistribute connected [ metric metric-value ] [ route-policy route-policy-name ]
  • process-id [ match { external | internal }] [ metric metric-value ] [ route-policy route-policy-name ]
  • redistribute isis process-id [ level { 1 | 1-inter-area | 2 }] [ metric metric-value ] [ route-policy route-policy-name ]
  • redistribute ospf process-id [ match { external [ 1 | 2 ] | internal | nssa-external [ 1 | 2 ]}] [ metric metric-value ] [ route-policy route-policy-name ]

Applies the cost community to the attach point (route policy).

Step 7

Do one of the following:

  • redistribute ospfv3 process-id [ match { external [ 1 | 2 ] | internal | nssa-external [ 1 | 2 ]}] [ metric metric-value ] [ route-policy route-policy-name ]
  • redistribute rip [ metric metric-value ] [ route-policy route-policy-name ]
  • redistribute static [ metric metric-value ] [ route-policy route-policy-name ]
  • network { ip-address/prefix-length | ip-address mask } [ route-policy route-policy-name ]
  • neighbor ip-address remote-as as-number
  • route-policy route-policy-name { in | out }

Step 8

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.

Step 9

show bgp ip-address

Example:

RP/0/RP0/CPU0:router# show bgp 172.168.40.24

Displays the cost community in the following format:

Cost: POI : cost-community-ID : cost-number


Configure BGP Community and Extended-Community Advertisements

Perform this task to specify that community/extended-community attributes should be sent to an eBGP neighbor. These attributes are not sent to an eBGP neighbor by default. By contrast, they are always sent to iBGP neighbors. This section provides examples on how to enable sending community attributes. The send-community-ebgp keyword can be replaced by the send-extended-community-ebgp keyword to enable sending extended-communities.

If the send-community-ebgp command is configured for a neighbor group or address family group, all neighbors using the group inherit the configuration. Configuring the command specifically for a neighbor overrides inherited values.


Note


BGP community and extended-community filtering cannot be configured for iBGP neighbors. Communities and extended-communities are always sent to iBGP neighbors under VPNv4, MDT, IPv4, and IPv6 address families.


Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:
RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

neighbor ip-address

Example:
RP/0/RP0/CPU0:router(config-bgp)# neighbor 172.168.40.24

Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address as a BGP peer.

Step 4

remote-as as-number

Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 2002 

Creates a neighbor and assigns a remote autonomous system number to it.

Step 5

address-family {ipv4 {labeled-unicast | unicast | mdt | | mvpn | rt-filter | tunnel } | ipv6 {labeled-unicast | mvpn | unicast }}

Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family ipv6 unicast

Enters neighbor address family configuration mode for the specified address family. Use either ipv4 or ipv6 address family keyword with one of the specified address family sub mode identifiers.

IPv6 address family mode supports these sub modes:
  • labeled-unicast

  • mvpn

  • unicast

IPv4 address family mode supports these sub modes:
  • labeled-unicast

  • mdt

  • mvpn

  • rt-filter

  • tunnel

  • unicast

Step 6

Use one of these commands:

  • send-community-ebgp
  • send-extended-community-ebgp
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# send-community-ebgp

or

RP/0/RP0/CPU0:router(config-bgp-nbr-af)# send-extended-community-ebgp

Specifies that the router send community attributes or extended community attributes (which are disabled by default for eBGP neighbors) to a specified eBGP neighbor.

Step 7

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Configuring BGP Large Communities

BGP communities provide a way to group destinations and apply routing decisions such as acceptance, rejection, preference, or redistribution on a group of destinations using community attributes. BGP community attributes are variable length attributes consisting of a set of one or more 4-byte values which are split into two parts of 16 bits. The higher-order 16 bits represents the AS number and the lower order bits represents a locally defined value assigned by the operator of the AS.

Since the adoption of 4-byte ASNs (RFC6793), the BGP communities attribute can no longer accommodate the 4 byte ASNs as you need more than 4 bytes to encode the 4-byte ASN and an AS specific value that you want to tag with the route. Although BGP extended community permits a 4-byte AS to be encoded as the global administrator field, the local administrator field has only 2-byte of available space. So, 6-byte extended community attribute is also unsuitable. To overcome this limitation, you can configure a 12-byte BGP large community which is an optional attribute that provides the most significant 4-byte value to encode autonomous system number as the global administrator and the remaining two 4-byte assigned numbers to encode the local values.

Similar to BGP communities, routers can apply BGP large communities to BGP routes by using route policy languages (RPL) and other routers can then perform actions based on the community that is attached to the route. The policy language provides sets as a container for groups of values for matching purposes.

When large communities are specified in other commands, they are specified as three non negative decimal integers separated by colons. For example, 1:2:3. Each integer is stored in 32 bits. The possible range for each integer is 0 to 4294967295.

In route-policy statements, each integer in the BGP large community can be replaced by any of the following expressions :

  • [x..y] — This expression specifies a range between x and y, inclusive.

  • * —This expression stands for any number.

  • peeras — This expression is replaced by the AS number of the neigbhor from which the community is received or to which the community is sent, as appropriate.

  • not-peeras —This expression matches any number other than the peeras.

  • private-as — This expression specifies any number in the private ASN range: [64512..65534] and [4200000000..4294967294].

These expressions can be also used in policy-match statements.

IOS regular expression (ios-regex) and DFA style regular expression (dfa-regex) can be used in any of the large-community policy match and delete statements. For example, the IOS regular expression ios-regex '^5:.*:7$' is equivalent to the expression 5:*:7.

The send-community-ebgp command is extended to include BGP large communities. This command is required for the BGP speaker to send large communities to ebgp neighbors.

Restrictions and Guidelines

The following restrictions and guidelines apply for BGP large communities:

  • All functionalities of the BGP community attribute is available for the BGP large-community attribute.

  • The send-community-ebgp command is required for the BGP speaker to send large communities to ebgp neighbors.

  • There are no well-known large-communities.

  • The peeras expression cannot be used in a large-community-set.

  • The peeras expression can only be used in large-community match or delete statements that appear in route policies that are applied at the neighbor-in or neighbor-out attach points.

  • The not-peeras expression cannot be used in a large-community-set or in policy set statements.

Configuration Example: Large Community Set

A large-community set defines a set of large communities. Named large-community sets are used in route-policy match and set statements.

This example shows how to create a named large-community set.

RP/0/RP0/CPU0:router(config)# large-community-set catbert
RP/0/RP0/CPU0:router(config-largecomm)#  1: 2: 3,
RP/0/RP0/CPU0:router(config-largecomm)#  peeras:2:3
RP/0/RP0/CPU0:router(config-largecomm)# end-set 
Configuration Example: Set Large Community

The following example shows how to set the BGP large community attribute in a route, using the set large-community {large-community-set-name | inline-large-community-set | parameter } [additive ] command. You can specify a named large-community-set or an inline set. The additive keyword retains the large communities already present in the route and adds the new set of large communities. However the additive keyword does not result in duplicate entries.

If a particular large community is attached to a route and you specify the same large community again with the additive keyword in the set statement, then the specified large community is not added again. The merging operation removes duplicate entries. This also applies to the peeras keyword.

The peeras expression in the example is replaced by the AS number of the neighbor from which the BGP large community is received or to which the community is sent, as appropriate.

RP/0/RP0/CPU0:router(config)# route-policy mordac 
RP/0/RP0/CPU0:router(config-rpl)# set large-community (1:2:3, peeras:2:3)
RP/0/RP0/CPU0:router(config-rpl)# end-set
RP/0/RP0/CPU0:router(config)# large-community-set catbert
RP/0/RP0/CPU0:router(config-largecomm)#  1: 2: 3,
RP/0/RP0/CPU0:router(config-largecomm)#  peeras:2:3
RP/0/RP0/CPU0:router(config-largecomm)# end-set
RP/0/RP0/CPU0:router(config)# route-policy wally
RP/0/RP0/CPU0:router(config-rpl)# set large-community catbert additive 
RP/0/RP0/CPU0:router(config-rpl)# end-set

In this example, if the route-policy mordac is applied to a neighbor, the ASN of which is 1, then the large community (1:2:3) is set only once.


Note


You should configure the send-community-ebgp command to send large communities to ebgp neighbors.


Configuration Example: Large Community Matches-any

The following example shows how to configure a route policy to match any element of a large -community set. This is a boolean condition and returns true if any of the large communities in the route match any of the large communities in the match condition.

RP/0/RP0/CPU0:router(config)# route-policy elbonia
RP/0/RP0/CPU0:router(config-rpl)# if large-community matches-any (1:2:3, 4:5:*) then
RP/0/RP0/CPU0:router(config-rpl)#   set local-preference 94
RP/0/RP0/CPU0:router(config-rpl)#  endif
RP/0/RP0/CPU0:router(config-rpl)# end-policy
Configuration Example: Large Community Matches-every

The following example shows how to configure a route policy where every match specification in the statement must be matched by at least one large community in the route.

RP/0/RP0/CPU0:router(config)# route-policy bob
RP/0/RP0/CPU0:router(config-rpl)# if large-community matches-every (*:*:3, 4:5:*) then
RP/0/RP0/CPU0:router(config-rpl)#   set local-preference 94
RP/0/RP0/CPU0:router(config-rpl)#  endif
RP/0/RP0/CPU0:router(config-rpl)# end-policy

In this example, routes with these sets of large communities return TRUE:

  • (1:1:3, 4:5:10)

  • (4:5:3) —This single large community matches both specifications.

  • (1:1:3, 4:5:10, 7:6:5)

Routes with the following set of large communities return FALSE:

(1:1:3, 5:5:10)—The specification (4:5:*) is not matched.

Configuration Example: Large Community Matches-within

The following example shows how to configure a route policy to match within a large community set. This is similar to the large-community matches-any command but every large community in the route must match at least one match specification. Note that if the route has no large communities, then it matches.

RP/0/RP0/CPU0:router(config)# route-policy bob
RP/0/RP0/CPU0:router(config-rpl)# if large-community matches-within (*:*:3, 4:5:*) then
RP/0/RP0/CPU0:router(config-rpl)#   set local-preference 103
RP/0/RP0/CPU0:router(config-rpl)#  endif
RP/0/RP0/CPU0:router(config-rpl)# end-policy

For example, routes with these sets of large communities return TRUE:

  • (1:1:3, 4:5:10)

  • (4:5:3)

  • (1:2:3, 6:6:3, 9:4:3)

Routes with this set of large communities return FALSE:

(1:1:3, 4:5:10, 7:6:5) —The large community (7:6:5) does not match

Configuration Example: Community Matches-within

The following example shows how to configure a route policy to match within the elements of a community set. This command is similar to the community matches-any command, but every community in the route must match at least one match specification. If the route has no communities, then it matches.

RP/0/RP0/CPU0:router(config)# route-policy bob
RP/0/RP0/CPU0:router(config-rpl)# if community matches-within (*:3, 5:*)  then
RP/0/RP0/CPU0:router(config-rpl)#   set local-preference 94
RP/0/RP0/CPU0:router(config-rpl)#  endif
RP/0/RP0/CPU0:router(config-rpl)# end-policy

For example, routes with these sets of communities return TRUE:

  • (1:3, 5:10)

  • (5:3)

  • (2:3, 6:3, 4:3)

Routes with this set of communities return FALSE:

(1:3, 5:10, 6:5) —The community (6:5) does not match.

Configuration Example: Large Community Is-empty

The following example shows using the large-community is-empty clause to filter routes that do not have the large-community attribute set.

RP/0/RP0/CPU0:router(config)# route-policy lrg_comm_rp4
RP/0/RP0/CPU0:router(config-rpl)# if large-community is-empty then
RP/0/RP0/CPU0:router(config-rpl)#   set local-preference 104
RP/0/RP0/CPU0:router(config-rpl)#  endif
RP/0/RP0/CPU0:router(config-rpl)# end-policy

Configuration Example: Attribute Filter Group

The following example shows how to configure and apply the attribute-filter group with large-community attributes for a BGP neighbor. The filter specifies the BGP path attributes and an action to take when BGP update message is received. If an update message is received from the BGP neighbor that contains any of the specified attributes, then the specified action is taken. In this example, the attribute filter named dogbert is created and applied to the BGP neighbor 10.0.1.101. It specifies the large community attribute and the action of discard. That means, if the large community BGP path attribute is received in a BGP UPDATE message from the neighbor 10.0.1.101 then the attribute will be discarded before further processing of the message.


RP/0/RP0/CPU0:router(config)# router bgp 100
RP/0/RP0/CPU0:router(config-bgp)# attribute-filter group dogbert
RP/0/RP0/CPU0:router(config-bgp-attrfg)# attribute LARGE-COMMUNITY discard
RP/0/RP0/CPU0:router(config-bgp-attrfg)# neighbor 10.0.1.101
RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 6461
RP/0/RP0/CPU0:router(config-bgp-nbr)# update in filtering
RP/0/RP0/CPU0:router(config-nbr-upd-filter)# attribute-filter group dogbert

Configuration Example: Deleting Large Community

The following example shows how to delete specified BGP large-communities from a route policy using the delete large-community command.


RP/0/RP0/CPU0:router(config)# route-policy lrg_comm_rp2
RP/0/RP0/CPU0:router(config-rpl)# delete large-community in (ios-regex '^100000:’)  
RP/0/RP0/CPU0:router(config-rpl)# delete large-community all
RP/0/RP0/CPU0:router(config-rpl)# delete large-community not in (peeras:*:*, 41289:*:*)
Verification

This example displays the routes with large-communities given in the show bgp large-community list-of-large-communities [exact-match ] command. If the optional keyword exact-match is used, then the listed routes will contain only the specified large communities. Otherwise, the displayed routes may contain additional large communities.

RP/0/0/CPU0:R1# show bgp large-community 1:2:3 5:6:7
Thu Mar 23 14:40:33.597 PDT
BGP router identifier 4.4.4.4, local AS number 3
BGP generic scan interval 60 secs
Non-stop routing is enabled
BGP table state: Active
Table ID: 0xe0000000   RD version: 66
BGP main routing table version 66
BGP NSR Initial initsync version 3 (Reached)
BGP NSR/ISSU Sync-Group versions 66/0
BGP scan interval 60 secs

Status codes: s suppressed, d damped, h history, * valid, > best
              i - internal, r RIB-failure, S stale, N Nexthop-discard
Origin codes: i - IGP, e - EGP, ? - incomplete
   Network            Next Hop            Metric LocPrf Weight Path
* 10.0.0.3/32         10.10.10.3               0     94      0 ?
* 10.0.0.5/32         10.11.11.5               0             0 5 ?

This example displays the large community attached to a network using the show bgp ip-address/ prefix-length command.

RP/0/0/CPU0:R4# show bgp 10.3.3.3/32
Thu Mar 23 14:36:15.301 PDT
BGP routing table entry for 10.3.3.3/32
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                 42          42
Last Modified: Mar 22 20:04:46.000 for 18:31:30
Paths: (1 available, best #1)
  Advertised to peers (in unique update groups):
    10.11.11.5
  Path #1: Received by speaker 0
  Advertised to peers (in unique update groups):
    10.11.11.5
  Local
    10.10.10.3 from 10.10.10.3 (10.3.3.3)
      Origin incomplete, metric 0, localpref 94, valid, internal, best, group-best
      Received Path ID 0, Local Path ID 0, version 42
      Community: 258:259 260:261 262:263 264:265
      Large Community: 1:2:3 5:6:7 4123456789:4123456780:4123456788

Redistribute iBGP Routes into IGP

Perform this task to redistribute iBGP routes into an Interior Gateway Protocol (IGP), such as Intermediate System-to-Intermediate System (IS-IS) or Open Shortest Path First (OSPF).


Note


Use of the bgp redistribute-internal command requires the clear route * command to be issued to reinstall all BGP routes into the IP routing table.



Caution


Redistributing iBGP routes into IGPs may cause routing loops to form within an autonomous system. Use this command with caution.


Procedure


Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:


RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

bgp redistribute-internal

Example:


RP/0/RP0/CPU0:router(config-bgp)# bgp redistribute-internal

Allows the redistribution of iBGP routes into an IGP, such as IS-IS or OSPF.

Step 4

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Redistribute IGPs to BGP

Perform this task to configure redistribution of a protocol into the VRF address family.

Even if Interior Gateway Protocols (IGPs) are used as the PE-CE protocol, the import logic happens through BGP. Therefore, all IGP routes have to be imported into the BGP VRF table.

Procedure


Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:


RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

vrf vrf-name

Example:


RP/0/RP0/CPU0:router(config-bgp)# vrf vrf_a

Enables BGP routing for a particular VRF on the PE router.

Step 4

address-family { ipv4 | ipv6 } unicast

Example:


RP/0/RP0/CPU0:router(config-vrf)# address-family ipv4 unicast

Specifies either an IPv4 or IPv6 address family unicast and enters address family configuration submode.

To see a list of all the possible keywords and arguments for this command, use the CLI help (?).

Step 5

Do one of the following:

  • redistribute connected [ metric metric-value ] [ route-policy route-policy-name ]
  • redistribute isis process-id [ level { 1 | 1-inter-area | 2 }] [ metric metric-value ] [ route-policy route-policy-name ]
  • redistribute ospf process-id [ match { external [ 1 | 2 ] | internal | nssa-external [ 1 | 2 ]}] [ metric metric-value ] [ route-policy route-policy-name ]
  • redistribute ospfv3 process-id [ match { external [ 1 | 2 ] | internal | nssa-external [ 1 | 2 ]}] [ metric metric-value ] [ route-policy route-policy-name ]
  • redistribute rip [ metric metric-value ] [ route-policy route-policy-name ]
  • redistribute static [ metric metric-value ] [ route-policy route-policy-name ]

Example:


RP/0/RP0/CPU0:router(config-bgp-vrf-af)# redistribute ospf 1 

Configures redistribution of a protocol into the VRF address family context.

The redistribute command is used if BGP is not used between the PE-CE routers. If BGP is used between PE-CE routers, the IGP that is used has to be redistributed into BGP to establish VPN connectivity with other PE sites. Redistribution is also required for inter-table import and export.

Step 6

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Update Groups

The BGP Update Groups feature contains an algorithm that dynamically calculates and optimizes update groups of neighbors that share outbound policies and can share the update messages. The BGP Update Groups feature separates update group replication from peer group configuration, improving convergence time and flexibility of neighbor configuration.

Monitor BGP Update Groups

This task displays information related to the processing of BGP update groups.

Procedure

show bgp [ ipv4 { unicast | multicast | all | tunnel } | ipv6 { unicast | all } | all { unicast | multicast | all labeled-unicast | tunnel } | vpnv4 unicast | vrf { vrf-name | all } [ ipv4 unicast ipv6 unicast ] | vpvn6 unicast ] update-group [ neighbor ip-address | process-id.index [ summary | performance-statistics ]]

Example:

RP/0/RP0/CPU0:router# show bgp update-group 0.0

Displays information about BGP update groups.

  • The ip-address argument displays the update groups to which that neighbor belongs.

  • The process-id.index argument selects a particular update group to display and is specified as follows: process ID (dot) index. Process ID range is from 0 to 254. Index range is from 0 to 4294967295.

  • The summary keyword displays summary information for neighbors in a particular update group.

  • If no argument is specified, this command displays information for all update groups (for the specified address family).

  • The performance-statistics keyword displays performance statistics for an update group.


Displaying BGP Update Groups: Example

The following is sample output from the show bgp update-group command run in EXEC configurationXR EXEC mode:


  
 show bgp update-group
  
  Update group for IPv4 Unicast, index 0.1:
    Attributes:
      Outbound Route map:rm
      Minimum advertisement interval:30
    Messages formatted:2, replicated:2
    Neighbors in this update group:
      10.0.101.92
  
  Update group for IPv4 Unicast, index 0.2:
    Attributes:
      Minimum advertisement interval:30
    Messages formatted:2, replicated:2
    Neighbors in this update group:
      10.0.101.91
  

L3VPN iBGP PE-CE

The L3VPN iBGP PE-CE feature helps establish an iBGP (internal Border Gateway Protocol) session between the provider edge (PE) and customer edge (CE) devices to exchange BGP routing information. A BGP session between two BGP peers is said to be an iBGP session if the BGP peers are in the same autonomous systems.

Restrictions for L3VPN iBGP PE-CE

The following restrictions apply to configuring L3VPN iBGP PE-CE:
  • When the iBGP PE CE feature is toggled and the neighbor no longer supports route-refresh or soft-reconfiguration inbound, a manual session flap must be done to see the change. When this occurs, the following message is displayed:
    RP/0/RP0/CPU0: %ROUTING-BGP-5-CFG_CHG_RESET: Internal VPN client configuration change on neighbor 10.10.10.1 requires HARD reset 
    (clear bgp 10.10.10.1) to take effect.
  • iBGP PE CE CLI configuration is not available for peers under default-VRF, except for neighbor/session-group.

  • This feature does not work on regular VPN clients (eBGP VPN clients).

  • Attributes packed inside the ATTR_SET reflects changes made by the inbound route-policy on the iBGP CE and does not reflect the changes made by the export route-policy for the specified VRF.

  • Different VRFs of the same VPN (that is, in different PE routers) that are configured with iBGP PE-CE peering sessions must use different Route Distinguisher (RD) values under respective VRFs. The iBGP PE CE feature does ot work if the RD values are the same for the ingress and egress VRF.

Configuring L3VPN iBGP PE-CE

L3VPN iBGP PE-CE can be enabled on the neighbor, neighbor-group, or session-group. To configure L3VPN iBGP PE-CE, follow these steps:

Before you begin

The CE must be an internal BGP peer.

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

vrf vrf-name

Example:

RP/0/RP0/CPU0:router(config-bgp)# vrf blue

Configures a VRF instance.

Step 4

neighbor ip-address internal-vpn-client

Example:

RP/0/RP0/CPU0:router(config-bgp-vrf)# neighbor 10.0.0.0  internal-vpn-client

Configures a CE neighboring device with which to exchange routing information. The neighbor internal-vpn-client command stacks the iBGP-CE neighbor path in the VPN attribute set.

Step 5

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.

Step 6

show bgp vrf vrf-name neighbors ip-address

Displays whether the iBGP PE-CE feature is enabled for the VRF CE peer, or not.

Step 7

show bgp { vpnv4| vpnv6 } unicast rd

Displays the ATTR_SET attributes in the command output when the L3VPN iBGP PE-CE is enabled on a CE.


Example
Example: Configuring L3VPN iBGP PE-CE
The following example shows how to configure L3VPN iBGP PE-CE:

R1(config-bgp-vrf-nbr)#neighbor 10.10.10.1 ?
. . .
 internal-vpn-client     Preserve iBGP CE neighbor path in ATTR_SET across VPN core
. . .
R1(config-bgp-vrf-nbr)#neighbor 10.10.10.1 internal-vpn-client
router bgp 65001
 bgp router-id 100.100.100.2
 address-family ipv4 unicast
address-family vpnv4 unicast
 !
 vrf ce-ibgp
  rd 65001:100
  address-family ipv4 unicast
  !
  neighbor 10.10.10.1
   remote-as 65001
   internal-vpn-client

The following is an example of the output of the show bgp vrf vrf-name neighbors ip-address command when the L3VPN iBGP PE-CE is enabled on a CE peer:

R1#show bgp vrf ce-ibgp neighbors 10.10.10.1
BGP neighbor is 10.10.10.1, vrf ce-ibgp
 Remote AS 65001, local AS 65001, internal link
 Remote router ID 100.100.100.1
  BGP state = Established, up for 00:00:19
  . . .
 Multi-protocol capability received
  Neighbor capabilities:
    Route refresh: advertised (old + new) and received (old + new)
    4-byte AS: advertised and received
    Address family IPv4 Unicast: advertised and received
CE attributes will be preserved across the core 
  Received 2 messages, 0 notifications, 0 in queue
  Sent 2 messages, 0 notifications, 0 in queue
  . . .

The following is an example of the output of the show bgp vpn4/vpn6 unicast rd command when the L3VPN iBGP PE-CE is enabled on a CE peer:

BGP routing table entry for 1.1.1.0/24, Route Distinguisher: 200:300
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                 10          10
Last Modified: Aug 28 13:11:17.000 for 00:01:00
Paths: (1 available, best #1)
  Advertised to update-groups (with more than one peer):
    0.2 
Path #1: Received by speaker 0
  Advertised to update-groups (with more than one peer):
    0.2 
  Local, (Received from a RR-client)
    20.20.20.2 from 20.20.20.2 (100.100.100.2)
      Received Label 24000
      Origin IGP, localpref 100, valid, internal, best, group-best, import-candidate, 
						not-in-vrf Received Path ID 0, Local Path ID 1, version 10
      Extended community: RT:228:237 
     ATTR-SET [
        Origin-AS: 200
        AS-Path: 51320 52325 59744 12947 21969 50346 18204 36304 41213 23906 33646
        Origin: incomplete
        Metric: 204
        Local-Pref: 234
        Aggregator: 304 34.3.3.3
        Atomic Aggregator
        Community: 1:60042 2:41661 3:47008 4:9280 5:39778 6:1069 7:15918 8:8994 9:52701 
10:10268 11:26276 12:8506 13:7131 14:65464 15:14304 16:33615 17:54991 18:40149 19:19401
        Extended community: RT:100:1 RT:1.1.1.1:1] 

Flow-tag propagation

The flow-tag propagation feature enables you to establish a co-relation between route-policies and user-policies. Flow-tag propagation using BGP allows user-side traffic-steering based on routing attributes such as, AS number, prefix lists, community strings and extended communities. Flow-tag is a logical numeric identifier that is distributed through RIB as one of the routing attribute of FIB entry in the FIB lookup table. A flow-tag is instantiated using the 'set' operation from RPL and is referenced in the C3PL PBR policy, where it is associated with actions (policy-rules) against the flow-tag value.

You can use flow-tag propagation to:

  • Classify traffic based on destination IP addresses (using the Community number) or based on prefixes (using Community number or AS number).

  • Select a TE-group that matches the cost of the path to reach a service-edge based on customer site service level agreements (SLA).

  • Apply traffic policy (TE-group selection) for specific customers based on SLA with its clients.

  • Divert traffic to application or cache server.

Restrictions for Flow-Tag Propagation

Some restrictions are placed with regard to using Quality-of-service Policy Propagation Using Border Gateway Protocol (QPPB) and flow-tag feature together. These include:

  • A route-policy can have either 'set qos-group' or 'set flow-tag,' but not both for a prefix-set.
  • Route policy for qos-group and route policy flow-tag cannot have overlapping routes. The QPPB and flow tag features can coexist (on same as well as on different interfaces) as long as the route policy used by them do not have any overlapping route.
  • Mixing usage of qos-group and flow-tag in route-policy and policy-map is not recommended.

Source and destination-based flow tag

The source-based flow tag feature allows you to match packets based on the flow-tag assigned to the source address of the incoming packets. Once matched, you can then apply any supported PBR action on this policy.

Configure Source and Destination-based Flow Tag

This task applies flow-tag to a specified interface. The packets are matched based on the flow-tag assigned to the source address of the incoming packets.


Note


You will not be able to enable both QPPB and flow tag feature simultaneously on an interface.
Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

interface type interface-path-id

Example:

RP/0/RP0/CPU0:router(config-if)# interface 

Enters interface configuration mode and associates one or more interfaces to the VRF.

Step 3

ipv4 | ipv6 bgp policy propagation input flow-tag{destination | source}

Example:

RP/0/RP0/CPU0:router(config-if)# ipv4 bgp policy propagation input flow-tag source

Enables flow-tag policy propagation on source or destination IP address on an interface.

Step 4

Use the commit or end command.

commit —Saves the configuration changes, and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration mode, without committing the configuration changes.


Example
The following show commands display outputs with PBR policy applied on the router:
show running-config interface gigabitEthernet 0/0/0/12
Thu Feb 12 01:51:37.820 UTC
interface GigabitEthernet0/0/0/12
 service-policy type pbr input flowMatchPolicy
 ipv4 bgp policy propagation input flow-tag source
 ipv4 address 192.5.1.2 255.255.255.0
!

RP/0/RSP0/CPU0:ASR9K-0#show running-config policy-map type pbr flowMatchPolicy 
Thu Feb 12 01:51:45.776 UTC
policy-map type pbr flowMatchPolicy
 class type traffic flowMatch36 
  transmit
 ! 
 class type traffic flowMatch38 
  transmit
 ! 
 class type traffic class-default 
 ! 
 end-policy-map
! 

RP/0/RSP0/CPU0:ASR9K-0#show running-config class-map type traffic flowMatch36
Thu Feb 12 01:52:04.838 UTC
class-map type traffic match-any flowMatch36
 match flow-tag 36 
 end-class-map
!

BGP Keychains

BGP keychains enable keychain authentication between two BGP peers. The BGP endpoints must both comply with draft-bonica-tcp-auth-05.txt and a keychain on one endpoint and a password on the other endpoint does not work.

BGP is able to use the keychain to implement hitless key rollover for authentication. Key rollover specification is time based, and in the event of clock skew between the peers, the rollover process is impacted. The configurable tolerance specification allows for the accept window to be extended (before and after) by that margin. This accept window facilitates a hitless key rollover for applications (for example, routing and management protocols).

The key rollover does not impact the BGP session, unless there is a keychain configuration mismatch at the endpoints resulting in no common keys for the session traffic (send or accept).

Configure Keychains for BGP

Keychains provide secure authentication by supporting different MAC authentication algorithms and provide graceful key rollover. Perform this task to configure keychains for BGP. This task is optional.


Note


If a keychain is configured for a neighbor group or a session group, a neighbor using the group inherits the keychain. Values of commands configured specifically for a neighbor override inherited values.


Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

neighbor ip-address

Example:

RP/0/RP0/CPU0:router(config-bgp)# neighbor 172.168.40.24

Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address as a BGP peer.

Step 4

remote-as as-number

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 2002

Creates a neighbor and assigns a remote autonomous system number to it.

Step 5

keychain name

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# keychain kych_a

Configures keychain-based authentication.

Step 6

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Master Key Tuple Configuration

This feature specifies TCP Authentication Option (TCP-AO), which replaces the TCP MD5 option. TCP-AO uses the Message Authentication Codes (MACs), which provides the following:

  • Protection against replays for long-lived TCP connections

  • More details on the security association with TCP connections than TCP MD5

  • A larger set of MACs with minimal other system and operational changes

TCP-AO is compatible with Master Key Tuple (MKT) configuration. TCP-AO also protects connections when using the same MKT across repeated instances of a connection. TCP-AO protects the connections by using traffic key that are derived from the MKT, and then coordinates changes between the endpoints.

Note


TCPAO and TCP MD5 are never permitted to be used simultaneously. TCP-AO supports IPv6, and is fully compatible with the proposed requirements for the replacement of TCP MD5.


Cisco provides the MKT configuration via the following configurations:
  • keychain configuration

  • tcp ao keychain configuration

The system translates each key, such "key_id" that is under a keychain, as MKT. The keychain configuration owns part of the configuration like secret, lifetimes, and algorithms. While the "tcp ao keychain" mode owns the TCP AO-specific configuration for an MKT (send_id and receive_id).

Keychain Configurations

Configuration Guidelines

In order to run a successful configuration, ensure that you follow the configuration guidelines:

  • An allowed value range for both Send_ID and Receive_ID is 0 to 255.

  • You can link only one keychain to an application neighbor.

  • Under the same keychain, if you configure the same send_id key again under the keys that have an overlapping lifetime, then the old key becomes unusable until you correct the configuration.

  • The system sends a warning message in the following scenarios:
    • If there is a change in Send_ID or Receive_ID.
    • If the corresponding key is currently active, and is in use by some connection.

  • BGP neighbor can ONLY use one of the authentication options:
    • MD5

    • EA

    • AO


    Note


    If you configure one of these options, the system rejects the other authentication options during the configuration time.


Configuration Guidelines for TCP AO BGP Neighbor

The configuration guidelines are:

  • Configure all the necessary configurations (key_string, MAC_algorithm, send_lifetime, accept_lifetime, send_id, receive_id) under key_id with the desired lifetime it wants to use the key_id for.

  • Configure a matching MKT in the peer side with exactly same lifetime.

  • Once a keychain-key is linked to tcp-ao, do not change the components of the key. If you want TCP to consider another key for use, you can configure that dynamically. Based on the ‘start-time’of send lifetime, TCP AO uses the key.

  • Send_ID and Receive_ID under a key_id (under a keychain) must have the same lifetime range. For example, send-lifetime==accept-lifetime.

    TCP considers only expiry of send-lifetime to transition to next active key and it does not consider accept-lifetime at all.

  • Do not configure a key with send-lifetime that is covered by another key’s send-lifetime.

    For example, if there is a key that is already configured with send-lifetime of “04:00:00 November 01, 2017 07:00:00 November 01, 2017” and the user now configures another key with send-lifetime of “05:00:00 November 01, 2017 06:00:00 November 01, 2017”, this might result into connection flap.

    TCP AO tries to transition back to the old key once the new key is expired. However, if the new key has already expired, TCP AO can’t use it, which might result in segment loss and hence connection flap.

  • Configure minimum of 15 minutes of overlapping time between the two overlapping keys. When a key expires, TCP does not use it and hence out-of-order segments with that key are dropped.

  • We recommend configuring send_id and receive_id to be same for a key_id for simplicity.

  • TCP does not have any restriction on the number of keychains and keys under a keychain. The system does not support more than 4000 keychains, any number higher than 4000 might result in unexpected behaviors.

Keychain Configuration

key chain <keychain_name>
   key <key_id>
      accept-lifetime <start-time> <end-time>
      key-string <master-key>
      send-lifetime <start-time> <end-time>
      cryptographic-algorithm <algorithm>
   !
!

TCP Configuration

TCP provides a new tcp ao submode that specifies SendID and ReceiveID per key_id per keychain.
tcp ao
    keychain <keychain_name1>
        key-id <key_id> send_id <0-255> receive_id <0-255>
        !
Example:
tcp ao
 keychain bgp_ao
  key 0 SendID 0 ReceiveID 0
  key 1 SendID 1 ReceiveID 1
  key 2 SendID 3 ReceiveID 4
 !
 keychain ldp_ao
  key 1 SendID 100 ReceiveID 200
  key 120 SendID 1 ReceiveID 1
 !

BGP Configurations

Applications like BGP provide the tcp-ao keychain and related information that it uses per neighbor. Following are the optional configurations per tcp-ao keychain:

  • include-tcp-options

  • accept-non-ao-connections

router bgp <AS-number>
neighbor <neighbor-ip>
  remote-as <remote-as-number>
  ao <keychain-name> include-tcp-options enable/disable  <accept-ao-mismatch-connections>
!

XML Configurations

BGP XML

TCP-AO XML

<?xml version="1.0" encoding="UTF-8"?>
<Request>
 <Set>
  <Configuration>
   <IP_TCP>
    <AO>
      <Enable>
       true
      </Enable>
      <KeychainTable>
        <Keychain>
         <Naming>
          <Name> bgp_ao_xml </Name>
         </Naming>
         <Enable>
          true
         </Enable>
          <KeyTable>
           <Key>
            <Naming>
             <KeyID> 0 </KeyID>
            </Naming>
             <SendID> 0 </SendID>
             <ReceiveID> 0 </ReceiveID>
           </Key>
          </KeyTable>
        </Keychain>
      </KeychainTable>
    </AO>
   </IP_TCP>
  </Configuration>
 </Set>
 <Commit/>
</Request>

BGP Nonstop Routing

The Border Gateway Protocol (BGP) Nonstop Routing (NSR) with Stateful Switchover (SSO) feature enables all bgp peerings to maintain the BGP state and ensure continuous packet forwarding during events that could interrupt service. Under NSR, events that might potentially interrupt service are not visible to peer routers. Protocol sessions are not interrupted and routing states are maintained across process restarts and switchovers.

BGP Nonstop Routing Reference for additional details.

Configure BGP Nonstop Routing

BGP Nonstop Routing (BGP NSR) is enabled by default. If BGP NSR is disabled, use the no nsr disable command to turn BGP NSR back on.

Note


In some scenarios, it is possible that some or all bgp sessions are not NSR-READY. The show redundancy command may still show that the bgp sessions are NSR-ready. Hence, we recommend that you verify the bgp nsr state by using the show bgp sessions command.


Disable BGP Nonstop Routing

Perform this task to disable BGP Nonstop Routing (NSR):

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the BGP AS number, and enters the BGP configuration mode, for configuring BGP routing processes.

Step 3

nsr disable

Example:

RP/0/RP0/CPU0:router(config-bgp)# nsr disable

Disables BGP Nonstop routing.

Step 4

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Disable BGP Nonstop Routing: Example

The following example shows how to disable BGP NSR:


 configure
 router bgp 120
 no nsr
 end

Re-enable BGP Nonstop Routing

If BGP Nonstop Routing (NSR) is disabled, use the following steps to turn BGP NSR back on using the following steps:

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the BGP AS number, and enters the BGP configuration mode, for configuring BGP routing processes.

Step 3

no nsr disable

Example:

RP/0/RP0/CPU0:router(config-bgp)# nsr disable

Enables BGP Nonstop routing.

Step 4

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Re-enable BGP Nonstop Routing: Example

The following example shows how to enable BGP NSR:


 configure
 router bgp 120
 nsr
 end

Accumulated Interior Gateway Protocol Attribute

The Accumulated Interior Gateway Protocol (AiGP)Attribute is an optional non-transitive BGP Path Attribute. The attribute type code for the AiGP Attribute is to be assigned by IANA. The value field of the AiGP Attribute is defined as a set of Type/Length/Value elements (TLVs). The AiGP TLV contains the Accumulated IGP Metric.

The AiGP feature is required in the 3107 network to simulate the current OSPF behavior of computing the distance associated with a path. OSPF/LDP carries the prefix/label information only in the local area. Then, BGP carries the prefix/lable to all the remote areas by redistributing the routes into BGP at area boundaries. The routes/labels are then advertised using LSPs. The next hop for the route is changed at each ABR to local router which removes the need to leak OSPF routes across area boundaries. The bandwidth available on each of the core links is mapped to OSPF cost, hence it is imperative that BGP carries this cost correctly between each of the PEs. This functionality is achieved by using the AiGP.

Originate Prefixes with AiGP

Perform this task to configure origination of routes with the AiGP metric:

Before you begin

Origination of routes with the accumulated interior gateway protocol (AiGP) metric is controlled by configuration. AiGP attributes are attached to redistributed routes that satisfy following conditions:

  • The protocol redistributing the route is enabled for AiGP.

  • The route is an interior gateway protocol (iGP) route redistributed into border gateway protocol (BGP). The value assigned to the AiGP attribute is the value of iGP next hop to the route or as set by a route-policy.

  • The route is a static route redistributed into BGP. The value assigned is the value of next hop to the route or as set by a route-policy.

  • The route is imported into BGP through network statement. The value assigned is the value of next hop to the route or as set by a route-policy.

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

route-policy aigp_policy

Example:
RP/0/RP0/CPU0:router(config)# route-policy aip_policy

Enters route-policy configuration mode and sets the route-policy

Step 3

set aigp-metric igp-cost

Example:
RP/0/RP0/CPU0:router(config-rpl)# set aigp-metric igp-cost

Sets the internal routing protocol cost as the aigp metric.

Step 4

exit

Example:
RP/0/RP0/CPU0:router(config-rpl)# exit

Exits route-policy configuration mode.

Step 5

router bgp as-number

Example:
RP/0/RP0/CPU0:router(config)# router bgp 100

Specifies the BGP AS number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 6

address-family {ipv4 | ipv6 } unicast

Example:
RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 unicast

Specifies either the IPv4 or IPv6 address family and enters address family configuration submode.

Step 7

redistribute ospf osp route-policy plcy_name metric value

Example:
RP/0/RP0/CPU0:router(config-bgp-af)#redistribute ospf osp route-policy aigp_policy metric 1

Allows the redistribution of AiBGP metric into OSPF.

Step 8

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Originating Prefixes With AiGP: Example

The following is a sample configuration for originating prefixes with the AiGP metric attribute:


route-policy aigp-policy
  set aigp-metric 4
  set aigp-metric igp-cost
end-policy
!
router bgp 100
 address-family ipv4 unicast
  network 10.2.3.4/24 route-policy aigp-policy
  redistribute ospf osp1 metric 4 route-policy aigp-policy
 !
!
end

Configure BGP Accept Own

The BGP Accept Own feature allows you to handle self-originated VPN routes, which a BGP speaker receives from a route-reflector (RR). A 'self-originated' route is one which was originally advertized by the speaker itself. As per BGP protocol [RFC4271], a BGP speaker rejects advertisements that were originated by the speaker itself. However, the BGP Accept Own mechanism enables a router to accept the prefixes it has advertised, when reflected from a route-reflector that modifies certain attributes of the prefix. A special community called ACCEPT-OWN is attached to the prefix by the route-reflector, which is a signal to the receiving router to bypass the ORIGINATOR_ID and NEXTHOP/MP_REACH_NLRI check. Generally, the BGP speaker detects prefixes that are self-originated through the self-origination check (ORIGINATOR_ID, NEXTHOP/MP_REACH_NLRI) and drops the received updates. However, with the Accept Own community present in the update, the BGP speaker handles the route.

One of the applications of BGP Accept Own is auto-configuration of extranets within MPLS VPN networks. In an extranet configuration, routes present in one VRF is imported into another VRF on the same PE. Normally, the extranet mechanism requires that either the import-rt or the import policy of the extranet VRFs be modified to control import of the prefixes from another VRF. However, with Accept Own feature, the route-reflector can assert that control without the need for any configuration change on the PE. This way, the Accept Own feature provides a centralized mechanism for administering control of route imports between different VRFs.


Note


BGP Accept Own is supported only for VPNv4 and VPNv6 address families in neighbor configuration mode.


Perform this task to configure BGP Accept Own:

Procedure


Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)#router bgp 100

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

neighbor ip-address

Example:

RP/0/RP0/CPU0:router(config-bgp)#neighbor 10.1.2.3

Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address as a BGP peer.

Step 4

remote-as as-number

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)#remote-as 100

Assigns a remote autonomous system number to the neighbor.

Step 5

update-source type interface-path-id

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)#update-source Loopback0

Allows sessions to use the primary IP address from a specific interface as the local address when forming a session with a neighbor.

Step 6

address-family {vpnv4 unicast | vpnv6 unicast }

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)#address-family vpnv6 unicast

Specifies the address family as VPNv4 or VPNv6 and enters neighbor address family configuration mode.

Step 7

accept-own [inheritance-disable ]

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr-af)#accept-own

Enables handling of self-originated VPN routes containing Accept_Own community.

Use the inheritance-disable keyword to disable the "accept own" configuration and to prevent inheritance of "acceptown" from a parent configuration.


BGP Accept Own Configuration: Example

In this configuration example:
  • PE11 is configured with Customer VRF and Service VRF.

  • OSPF is used as the IGP.

  • VPNv4 unicast and VPNv6 unicast address families are enabled between the PE and RR neighbors and IPv4 and IPv6 are enabled between PE and CE neighbors.

The Accept Own configuration works as follows:
  1. CE1 originates prefix X.

  2. Prefix X is installed in customer VRF as (RD1:X).

  3. Prefix X is advertised to IntraAS-RR11 as (RD1:X, RT1).

  4. IntraAS-RR11 advertises X to InterAS-RR1 as (RD1:X, RT1).

  5. InterAS-RR1 attaches RT2 to prefix X on the inbound and ACCEPT_OWN community on the outbound and advertises prefix X to IntraAS-RR31.

  6. IntraAS-RR31 advertises X to PE11.

  7. PE11 installs X in Service VRF as (RD2:X,RT1, RT2, ACCEPT_OWN).

This example shows how to configure BGP Accept Own on a PE router.

router bgp 100
 neighbor 45.1.1.1
   remote-as 100
   update-source Loopback0
   address-family vpnv4 unicast
    route-policy pass-all in
    accept-own
    route-policy drop_111.x.x.x out
   !
   address-family vpnv6 unicast
    route-policy pass-all in
    accept-own
    route-policy drop_111.x.x.x out
   !
  !
This example shows an InterAS-RR configuration for BGP Accept Own.
router bgp 100
 neighbor 45.1.1.1
  remote-as 100
  update-source Loopback0
  address-family vpnv4 unicast
   route-policy rt_stitch1 in
   route-reflector-client
   route-policy add_bgp_ao out
  !
  address-family vpnv6 unicast
   route-policy rt_stitch1 in
   route-reflector-client
   route-policy add_bgp_ao out
  !
 !
extcommunity-set rt cs_100:1
  100:1
end-set
!
extcommunity-set rt cs_1001:1
  1001:1
end-set
!
route-policy rt_stitch1
  if extcommunity rt matches-any cs_100:1 then
    set extcommunity rt cs_1000:1 additive
 endif
end-policy
!
route-policy add_bgp_ao
  set community (accept-own) additive
end-policy
!

BGP Link-State

BGP Link-State (LS) is an Address Family Identifier (AFI) and Sub-address Family Identifier (SAFI) originally defined to carry interior gateway protocol (IGP) link-state information through BGP. The BGP Network Layer Reachability Information (NLRI) encoding format for BGP-LS and a new BGP Path Attribute called the BGP-LS attribute are defined in RFC7752. The identifying key of each Link-State object, namely a node, link, or prefix, is encoded in the NLRI and the properties of the object are encoded in the BGP-LS attribute.


Note


IGPs do not use BGP LS data from remote peers. BGP does not download the received BGP LS data to any other component on the router.

An example of a BGP-LS application is the Segment Routing Path Computation Element (SR-PCE). The SR-PCE can learn the SR capabilities of the nodes in the topology and the mapping of SR segments to those nodes. This can enable the SR-PCE to perform path computations based on SR-TE and to steer traffic on paths different from the underlying IGP-based distributed best-path computation.

The following figure shows a typical deployment scenario. In each IGP area, one or more nodes (BGP speakers) are configured with BGP-LS. These BGP speakers form an iBGP mesh by connecting to one or more route-reflectors. This way, all BGP speakers (specifically the route-reflectors) obtain Link-State information from all IGP areas (and from other ASes from eBGP peers).

Exchange Link State Information with BGP Neighbor

The following example shows how to exchange link-state information with a BGP neighbor:


Router# configure
Router(config)# router bgp 1
Router(config-bgp)# neighbor 10.0.0.2
Router(config-bgp-nbr)# remote-as 1
Router(config-bgp-nbr)# address-family link-state link-state
Router(config-bgp-nbr-af)# exit

IGP Link-State Database Distribution

A given BGP node may have connections to multiple, independent routing domains. IGP link-state database distribution into BGP-LS is supported for both OSPF and IS-IS protocols in order to distribute this information on to controllers or applications that desire to build paths spanning or including these multiple domains.

To distribute OSPFv2 link-state data using BGP-LS, use the distribute link-state command in router configuration mode.


Router# configure
Router(config)# router ospf 100
Router(config-ospf)# distribute link-state instance-id 32

Usage Guidelines and Limitations

  • BGP-LS supports IS-IS and OSPFv2.

  • The identifier field of BGP-LS (referred to as the Instance-ID) identifies the IGP routing domain where the NLRI belongs. The NLRIs representing link-state objects (nodes, links, or prefixes) from the same IGP routing instance must use the same Instance-ID value.

  • When there is only a single protocol instance in the network where BGP-LS is operational, we recommend configuring the Instance-ID value to 0.

  • Assign consistent BGP-LS Instance-ID values on all BGP-LS Producers within a given IGP domain.

  • NLRIs with different Instance-ID values are considered to be from different IGP routing instances.

  • Unique Instance-ID values must be assigned to routing protocol instances operating in different IGP domains. This allows the BGP-LS Consumer (for example, SR-PCE) to build an accurate segregated multi-domain topology based on the Instance-ID values, even when the topology is advertised via BGP-LS by multiple BGP-LS Producers in the network.

  • If the BGP-LS Instance-ID configuration guidelines are not followed, a BGP-LS Consumer may see duplicate link-state objects for the same node, link, or prefix when there are multiple BGP-LS Producers deployed. This may also result in the BGP-LS Consumers getting an inaccurate network-wide topology.

  • The following table defines the supported extensions to the BGP-LS address family for carrying IGP topology information (including SR information) via BGP. For more information on the BGP-LS TLVs, refer to Border Gateway Protocol - Link State (BGP-LS) Parameters.

Table 2. IOS XR Supported BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs
TLV Code Point Description Produced by IS-IS Produced by OSPFv2 Produced by BGP
256 Local Node Descriptors X X
257 Remote Node Descriptors X X
258 Link Local/Remote Identifiers X X
259 IPv4 interface address X X
260 IPv4 neighbor address X
261 IPv6 interface address X
262 IPv6 neighbor address X
263 Multi-Topology ID X
264 OSPF Route Type X
265 IP Reachability Information X X
266 Node MSD TLV X X
267 Link MSD TLV X X
512 Autonomous System X
513 BGP-LS Identifier X
514 OSPF Area-ID X
515 IGP Router-ID X X
516 BGP Router-ID TLV X
517 BGP Confederation Member TLV X
1024 Node Flag Bits X X
1026 Node Name X X
1027 IS-IS Area Identifier X
1028 IPv4 Router-ID of Local Node X X
1029 IPv6 Router-ID of Local Node X
1030 IPv4 Router-ID of Remote Node X X
1031 IPv6 Router-ID of Remote Node X
1034 SR Capabilities TLV X X
1035 SR Algorithm TLV X X
1036 SR Local Block TLV X X
1039 Flex Algo Definition (FAD) TLV X X
1044 Flex Algorithm Prefix Metric (FAPM) TLV X X
1088 Administrative group (color) X X
1089 Maximum link bandwidth X X
1090 Max. reservable link bandwidth X X
1091 Unreserved bandwidth X X
1092 TE Default Metric X X
1093 Link Protection Type X X
1094 MPLS Protocol Mask X X
1095 IGP Metric X X
1096 Shared Risk Link Group X X
1099 Adjacency SID TLV X X
1100 LAN Adjacency SID TLV X X
1101 PeerNode SID TLV X
1102 PeerAdj SID TLV X
1103 PeerSet SID TLV X
1114 Unidirectional Link Delay TLV X X
1115 Min/Max Unidirectional Link Delay TLV X X
1116 Unidirectional Delay Variation TLV X X
1117 Unidirectional Link Loss X X
1118 Unidirectional Residual Bandwidth X X
1119 Unidirectional Available Bandwidth X X
1120 Unidirectional Utilized Bandwidth X X
1122 Application-Specific Link Attribute TLV X X
1152 IGP Flags X X
1153 IGP Route Tag X X
1154 IGP Extended Route Tag X
1155 Prefix Metric X X
1156 OSPF Forwarding Address X
1158 Prefix-SID X X
1159 Range X X
1161 SID/Label TLV X X
1170 Prefix Attribute Flags X X
1171 Source Router Identifier X
1172 L2 Bundle Member Attributes TLV X
1173 Extended Administrative Group X X

Configure BGP Link-state

To exchange BGP link-state (LS) information with a BGP neighbor, perform these steps:

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 100

Specifies the BGP AS number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

address-family link-state link-state

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family link-state link-state

Distributes BGP link-state information to the specified neighbor.

Step 4

neighbor ip-address

Example:

RP/0/RP0/CPU0:router(config-bgp)# neighbor 10.0.0.2

Configures a CE neighbor. The ip-address argument must be a private address.

Step 5

remote-as as-number

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 1

Configures the remote AS for the CE neighbor.

Step 6

address-family link-state link-state

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family link-state link-state

Distributes BGP link-state information to the specified neighbor.

Step 7

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Example

router bgp 100
 address-family link-state link-state
 !
 neighbor 10.0.0.2
  remote-as 1
  address-family link-state link-state

Configure Domain Distinguisher

To configure unique identifier four-octet ASN, perform these steps:

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 100

Specifies the BGP AS number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

address-family link-state link-state

Example:

RP/0/RP0/CPU0:router(config-bgp)# address-family link-state link-state

Enters address-family link-state configuration mode.

Step 4

domain-distinguisher unique-id

Example:

RP/0/RP0/CPU0:router(config-bgp-af)# domain-distinguisher 1234:1.2.3.4

Configures unique identifier four-octet ASN. Range is from 1 to 4294967295.

Step 5

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


BGP Permanent Network

BGP permanent network feature supports static routing through BGP. BGP routes to IPv4 or IPv6 destinations (identified by a route-policy) can be administratively created and selectively advertised to BGP peers. These routes remain in the routing table until they are administratively removed. A permanent network is used to define a set of prefixes as permanent, that is, there is only one BGP advertisement or withdrawal in upstream for a set of prefixes. For each network in the prefix-set, a BGP permanent path is created and treated as less preferred than the other BGP paths received from its peer. The BGP permanent path is downloaded into RIB when it is the best-path.

The permanent-network command in global address family configuration mode uses a route-policy to identify the set of prefixes (networks) for which permanent paths is to be configured. The advertise permanent-network command in neighbor address-family configuration mode is used to identify the peers to whom the permanent paths must be advertised. The permanent paths is always advertised to peers having the advertise permanent-network configuration, even if a different best-path is available. The permanent path is not advertised to peers that are not configured to receive permanent path.

The permanent network feature supports only prefixes in IPv4 unicast and IPv6 unicast address-families under the default Virtual Routing and Forwarding (VRF).

Restrictions

These restrictions apply while configuring the permanent network:

  • Permanent network prefixes must be specified by the route-policy on the global address family.

  • You must configure the permanent network with route-policy in global address family configuration mode and then configure it on the neighbor address family configuration mode.

  • When removing the permanent network configuration, remove the configuration in the neighbor address family configuration mode and then remove it from the global address family configuration mode.

Configure BGP Permanent Network

Perform this task to configure BGP permanent network. You must configure at least one route-policy to identify the set of prefixes (networks) for which the permanent network (path) is to be configured.

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

prefix-set prefix-set-name

Example:

RP/0/RP0/CPU0:router(config)# prefix-set PERMANENT-NETWORK-IPv4
RP/0/RP0/CPU0:router(config-pfx)# 1.1.1.1/32,
RP/0/RP0/CPU0:router(config-pfx)# 2.2.2.2/32,
RP/0/RP0/CPU0:router(config-pfx)# 3.3.3.3/32
RP/0/RP0/CPU0:router(config-pfx)# end-set

Enters prefix set configuration mode and defines a prefix set for contiguous and non-contiguous set of bits.

Step 3

exit

Example:

RP/0/RP0/CPU0:router(config-pfx)# exit

Exits prefix set configuration mode and enters global configuration mode.

Step 4

route-policy route-policy-name

Example:

RP/0/RP0/CPU0:router(config)# route-policy POLICY-PERMANENT-NETWORK-IPv4
RP/0/RP0/CPU0:router(config-rpl)# if destination in PERMANENT-NETWORK-IPv4 then
RP/0/RP0/CPU0:router(config-rpl)# pass
RP/0/RP0/CPU0:router(config-rpl)# endif
 

Creates a route policy and enters route policy configuration mode, where you can define the route policy.

Step 5

end-policy

Example:

RP/0/RP0/CPU0:router(config-rpl)# end-policy

Ends the definition of a route policy and exits route policy configuration mode.

Step 6

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 100

Specifies the autonomous system number and enters the BGP configuration mode.

Step 7

address-family { ipv4 | ipv6 } unicast

Example:

RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 unicast

Specifies either an IPv4 or IPv6 address family unicast and enters address family configuration submode.

Step 8

permanent-network route-policy route-policy-name

Example:

RP/0/RP0/CPU0:router(config-bgp-af)# permanent-network route-policy POLICY-PERMANENT-NETWORK-IPv4

Configures the permanent network (path) for the set of prefixes as defined in the route-policy.

Step 9

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.

Step 10

show bgp {ipv4 | ipv6} unicast prefix-set

Example:

RP/0/RP0/CPU0:routershow bgp ipv4 unicast 

(Optional) Displays whether the prefix-set is a permanent network in BGP.


Advertise Permanent Network

Perform this task to identify the peers to whom the permanent paths must be advertised.

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 100

Specifies the autonomous system number and enters the BGP configuration mode.

Step 3

neighbor ip-address

Example:

RP/0/RP0/CPU0:router(config-bgp)# neighbor 10.255.255.254

Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address as a BGP peer.

Step 4

remote-as as-number

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 4713

Assigns the neighbor a remote autonomous system number.

Step 5

address-family { ipv4 | ipv6 } unicast

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family ipv4 unicast

Specifies either an IPv4 or IPv6 address family unicast and enters address family configuration submode.

Step 6

advertise permanent-network

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr-af)# advertise permanent-network

Specifies the peers to whom the permanent network (path) is advertised.

Step 7

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.

Step 8

show bgp {ipv4 | ipv6} unicast neighbor ip-address

Example:

RP/0/RP0/CPU0:routershow bgp ipv4 unicast neighbor 10.255.255.254

(Optional) Displays whether the neighbor is capable of receiving BGP permanent networks.


Enable BGP Unequal Cost Recursive Load Balancing

Procedure

  Command or Action Purpose

Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:


RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

address-family { ipv4 | ipv6 } unicast

Example:


RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 unicast

Specifies either an IPv4 or IPv6 address family unicast and enters address family configuration submode.

To see a list of all the possible keywords and arguments for this command, use the CLI help (?).

Step 4

maximum-paths { ebgp | ibgp | eibgp } maximum [ unequal-cost ]

Example:


RP/0/RP0/CPU0:router(config-bgp-af)# maximum-paths ebgp 3

Configures the maximum number of parallel routes that BGP installs in the routing table.

  • ebgp maximum : Consider only eBGP paths for multipath.

  • ibgp maximum [ unequal-cost ]: Consider load balancing between iBGP learned paths.

  • eibgp maximum : Consider both eBGP and iBGP learned paths for load balancing. eiBGP load balancing always does unequal-cost load balancing.

When eiBGP is applied, eBGP or iBGP load balancing cannot be configured; however, eBGP and iBGP load balancing can coexist.

Step 5

exit

Example:


RP/0/RP0/CPU0:router(config-bgp-af)# exit

Exits the current configuration mode.

Step 6

neighbor ip-address

Example:


RP/0/RP0/CPU0:router(config-bgp)# neighbor 10.0.0.0

Configures a CE neighbor. The ip-address argument must be a private address.

Step 7

dmz-link-bandwidth

Example:


RP/0/RP0/CPU0:router(config-bgp-nbr)# dmz-link-bandwidth

Originates a demilitarized-zone (DMZ) link-bandwidth extended community for the link to an eBGP/iBGP neighbor.

Step 8

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.

DMZ Link Bandwidth for Unequal Cost Recursive Load Balancing

The demilitarized zone (DMZ) link bandwidth for unequal cost recursive load balancing feature provides support for unequal cost load balancing for recursive prefixes on local node using DMZ link bandwidth. Use the dmz-link-bandwidth command in BGP neighbor configuration mode and the bandwidth command in interface configuration mode to The unequal load balance is achieved.

When the PE router includes the link bandwidth extended community in its updates to the remote PE through the Multiprotocol Interior BGP (MP-iBGP) session (either IPv4 or VPNv4), the remote PE automatically does load balancing if the maximum-paths command is enabled.


Note


Unequal cost recursive load balancing happens across maximum eight paths only.


Enable BGP Unequal Cost Recursive Load Balancing
Procedure
  Command or Action Purpose

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

address-family { ipv4 | ipv6 } unicast

Example:

RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 unicast

Specifies either an IPv4 or IPv6 address family unicast and enters address family configuration submode.

To see a list of all the possible keywords and arguments for this command, use the CLI help (?).

Step 4

maximum-paths { ebgp | ibgp | eibgp } maximum [ unequal-cost ]

Example:

RP/0/RP0/CPU0:router(config-bgp-af)# maximum-paths ebgp 3

Configures the maximum number of parallel routes that BGP installs in the routing table.

  • ebgp maximum : Consider only eBGP paths for multipath.

  • ibgp maximum [ unequal-cost ]: Consider load balancing between iBGP learned paths.

  • eibgp maximum : Consider both eBGP and iBGP learned paths for load balancing. eiBGP load balancing always does unequal-cost load balancing.

When eiBGP is applied, eBGP or iBGP load balancing cannot be configured; however, eBGP and iBGP load balancing can coexist.

Step 5

exit

Example:

RP/0/RP0/CPU0:router(config-bgp-af)# exit

Exits the current configuration mode.

Step 6

neighbor ip-address

Example:

RP/0/RP0/CPU0:router(config-bgp)# neighbor 10.0.0.0

Configures a CE neighbor. The ip-address argument must be a private address.

Step 7

dmz-link-bandwidth

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# dmz-link-bandwidth

Originates a demilitarized-zone (DMZ) link-bandwidth extended community for the link to an eBGP/iBGP neighbor.

Step 8

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.

DMZ Link Bandwidth Over EBGP Peer

The demilitarized zone (DMZ) link bandwidth extended community is an optional non-transitive attribute; therefore, it is not advertised to eBGP peers by default but it is advertised only to iBGP peers. This extended community is meant for load balancing over multi-paths. However, Cisco IOS-XR enables advertising of the DMZ link bandwidth to an eBGP peer, or receiving the DMZ link bandwidth by an eBGP peer. This feature also gives the user the option to send the bandwidth unchanged, or take the accumulated bandwidth over all the egress links and advertise that to the upstream eBGP peer.

Use the ebgp-send-community-dmz command to send the community to eBGP peers. By default, the link bandwidth extended-community attribute associated with the best path is sent.

When the cumulative keyword is used, the value of the link bandwidth extended community is set to the sum of link bandwidth values of all the egress-multipaths. If the DMZ link bandwidth value of the multipaths is unknown, for instance, some paths do not have that attribute, then unequal cost load-balancing is not done at that node. However, the sum of the known DMZ link bandwidth values is calculated and sent to the eBGP peer.

Use the ebgp-recv-community-dmz command to receive the community from eBGP peers.


Note


The ebgp-send-community-dmz and ebgp-recv-community-dmz commands can be configured in the neigbor, neighbour-group, and session-group configuration mode.


Use the bgp bestpath as-path multipath-relax and bgp bestpath as-path ignore commands to handle multipath across different autonomous systems.

Sending and Receiving DMZ Link Bandwidth Extended Community over eBGP Peer
Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 100

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

neighbor ip-address

Example:

RP/0/RP0/CPU0:router(config-bgp)# neighbor 10.1.1.1

Enters the neighbor configuration mode for configuring BGP routing sessions.

Step 4

ebgp-send-extcommunity-dmz ip-address

Example:
RP/0/RP0/CPU0:router(config-bgp)# ebgp-send-extcommunity-dmz

Sends the DMZ link bandwidth extended community to the eBGP neighbor.

Note

 

Use the cumulative keyword with this command to set the value of the link bandwidth extended community to the sum of link bandwidth values of all the egress multipaths.

Step 5

exit

Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)# exit

Exits the neighbor configuration mode and enters into BGP configuration mode.

Step 6

neighbor ip-address

Example:

RP/0/RP0/CPU0:router(config-bgp)# neighbor 172.16.0.1

Enters the neighbor configuration mode for configuring BGP routing sessions.

Step 7

ebgp-recv-extcommunity-dmz

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# ebgp-recv-extcommunity-dmz

Receives the DMZ link bandwidth extended community to the eBGP neighbor.

Step 8

exit

Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)# exit

Exits the neighbor configuration mode and enters into BGP configuration mode.


DMZ Link Bandwidth: Example
The following examples shows how Router R1 sends DMZ link bandwidth extended communities to Router R2 over eBGP peer connection:

R1: sending router
------------------
neighbour 10.3.3.3
  remote-as 2
  ebgp-send-extcommunity-dmz
  address-family ipv4 unicast
   route-policy pass in
   route-policy pass out
  !

R2: Receiving router
--------------------
neighbor 192.0.2.1
  remote-as 3
  ebgp-recv-extcommunity-dmz
  address-family ipv4 unicast
   route-policy pass in
  !		
route-policy pass out		
!		
  
  

The following is a sample configuration that displays the DMZ link bandwidth configuration in the sending (R1) router:

RP/0/RP0/CPU0:router)# show bgp ipv4 unicast 10.1.1.1/32 detail
 
Path #1: Received by speaker 0
  Flags: 0x4000000001040003, import: 0x20
  Advertised to update-groups (with more than one peer):
    0.4 
  Advertised to peers (in unique update groups):
    20.0.0.1        
  3
    11.1.0.2 from 11.1.0.2 (11.1.0.2)
      Origin incomplete, metric 20, localpref 100, valid, external, best, group-best
      Received Path ID 0, Local Path ID 0, version 21
      Extended community: LB:3:192 
      Origin-AS validity: not-found

The following is a sample configuration that displays DMZ link bandwidth configuration in the receiving (R2) router:

RP/0/RP0/CPU0:router)# show bgp ipv4 unicast 10.1.1.1/32 detail
 
Paths: (1 available, best #1)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Not advertised to any peer
  1 3
    20.0.0.2 from 20.0.0.2 (10.0.0.81)
      Origin incomplete, localpref 100, valid, external, best, group-best
      Received Path ID 0, Local Path ID 0, version 17
      Extended community: LB:1:192 
      Origin-AS validity: not-found

BGP Prefix Origin Validation using RPKI

A BGP route associates an address prefix with a set of autonomous systems (AS) that identify the interdomain path the prefix has traversed in the form of BGP announcements. This set is represented as the AS_PATH attribute in BGP and starts with the AS that originated the prefix.

To help reduce well-known threats against BGP including prefix mis-announcing and monkey-in-the-middle attacks, one of the security requirements is the ability to validate the origination AS of BGP routes. The AS number claiming to originate an address prefix (as derived from the AS_PATH attribute of the BGP route) needs to be verified and authorized by the prefix holder.

The Resource Public Key Infrastructure (RPKI) is an approach to build a formally verifiable database of IP addresses and AS numbers as resources. The RPKI is a globally distributed database containing, among other things, information mapping BGP (internet) prefixes to their authorized origin-AS numbers. Routers running BGP can connect to the RPKI to validate the origin-AS of BGP paths.

Configure RPKI Cache-server

Perform this task to configure Resource Public Key Infrastructure (RPKI) cache-server parameters.

Configure the RPKI cache-server parameters in rpki-server configuration mode. Use the rpki server command in router BGP configuration mode to enter into the rpki-server configuration mode

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:
RP/0/RP0/CPU0:router(config)#router bgp 100

Specifies the BGP AS number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

rpki cache {host-name | ip-address }

Example:
RP/0/RP0/CPU0:router(config-bgp)#rpki server 10.2.3.4 

Enters rpki-server configuration mode and enables configuration of RPKI cache parameters.

Step 4

Use one of these commands:

  • transport ssh port port_number
  • transport tcp port port_number
Example:
RP/0/RP0/CPU0:router(config-bgp-rpki-server)#transport ssh port 22

Or

RP/0/RP0/CPU0:router(config-bgp-rpki-server)#transport tcp port 2

Specifies a transport method for the RPKI cache.

  • ssh —Select ssh to connect to the RPKI cache using SSH.

  • tcp —Select tcp to connect to the RPKI cache using TCP (unencrypted).

  • port port_number —Specify the port number for the RPKI cache transport over TCP and SSH protocols. The port number ranges from 1 to 65535.

Note

 
  • SSH supports custom ports in addition to the default port number 22.

  • You can set the transport to either TCP or SSH. Change of transport causes the cache session to flap.

Step 5

(Optional) username user_name

Example:
RP/0/RP0/CPU0:router(config-bgp-rpki-server)#username ssh_rpki_cache

Specifies a (SSH) username for the RPKI cache-server.

Step 6

(Optional) password

Example:
RP/0/RP0/CPU0:router(config-bgp-rpki-server)#password ssh_rpki_pass

Specifies a (SSH) password for the RPKI cache-server.

Note

 

The “username” and “password” configurations only apply if the SSH method of transport is active.

Step 7

preference preference_value

Example:
RP/0/RP0/CPU0:router(config-bgp-rpki-server)#preference 1

Specifies a preference value for the RPKI cache. Range for the preference value is 1 to 10. Setting a lower preference value is better.

Step 8

purge-time time

Example:
RP/0/RP0/CPU0:router(config-bgp-rpki-server)#purge-time 30

Configures the time BGP waits to keep routes from a cache after the cache session drops. Set purge time in seconds. Range for the purge time is 30 to 360 seconds.

Step 9

Use one of these commands.

  • refresh-time time
  • refresh-time off
Example:
RP/0/RP0/CPU0:router(config-bgp-rpki-server)#refresh-time 20

Or

RP/0/RP0/CPU0:router(config-bgp-rpki-server)#refresh-time off

Configures the time BGP waits in between sending periodic serial queries to the cache. Set refresh-time in seconds. Range for the refresh time is 15 to 3600 seconds.

Configure the off option to specify not to send serial-queries periodically.

Step 10

Use one these commands.

  • response-time time
  • response-time off
Example:
RP/0/RP0/CPU0:router(config-bgp-rpki-server)#response-time 30

Or

RP/0/RP0/CPU0:router(config-bgp-rpki-server)#response-time off

Configures the time BGP waits for a response after sending a serial or reset query. Set response-time in seconds. Range for the response time is 15 to 3600 seconds.

Configure the off option to wait indefinitely for a response.

Step 11

shutdown

Example:
RP/0/RP0/CPU0:router(config-bgp-rpki-server)#shutdown

Configures shut down of the RPKI cache.

Step 12

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Configure BGP Prefix Validation

Starting from Release 6.5.1, RPKI is disabled by default. From Release 6.5.1, use the following task to configure RPKI Prefix Validation.

Router(config)# router bgp 100
/* The bgp origin-as validation time and bgp origin-as validity signal ibgp commands are optional. */. 
Router(config-bgp)# bgp origin-as validation time 50
Router(config-bgp)# bgp origin-as validation time off
Router(config-bgp)# bgp origin-as validation signal ibgp
Router(config-bgp)# address-family ipv4 unicast
Router(config-bgp-af)# bgp origin-as validation enable

Use the following commands to verify the origin-as validation configuration:

Router# show bgp origin-as validity

Thu Mar 14 04:18:09.656 PDT
BGP router identifier 10.1.1.1, local AS number 1
BGP generic scan interval 60 secs
Non-stop routing is enabled
BGP table state: Active
Table ID: 0xe0000000   RD version: 514
BGP main routing table version 514
BGP NSR Initial initsync version 2 (Reached)
BGP NSR/ISSU Sync-Group versions 0/0
BGP scan interval 60 secs
Status codes: s suppressed, d damped, h history, * valid, > best
              i - internal, r RIB-failure, S stale, N Nexthop-discard
Origin codes: i - IGP, e - EGP, ? - incomplete
Origin-AS validation codes: V valid, I invalid, N not-found, D disabled
    Network                  Next Hop            Metric LocPrf Weight Path
 *> 209.165.200.223/27       0.0.0.0                  0         32768 ?

 *> 209.165.200.225/27       0.0.0.0                  0         32768 ?

 *> 19.1.2.0/24              0.0.0.0                  0         32768 ?

 *> 19.1.3.0/24              0.0.0.0                  0         32768 ?

 *> 10.1.2.0/24              0.0.0.0                  0         32768 ?

 *> 10.1.3.0/24              0.0.0.0                  0         32768 ?

 *> 10.1.4.0/24              0.0.0.0                  0         32768 ?

 *> 198.51.100.1/24          0.0.0.0                  0         32768 ?

 *> 203.0.113.235/24         0.0.0.0                  0         32768 ?

V*> 209.165.201.0/27        10.1.2.1                  0         4002 i

N*> 198.51.100.2/24         10.1.2.1                  0         4002 i

I*> 198.51.100.1/24         10.1.2.1                  0          4002 i

 *> 192.0.2.1.0/24          0.0.0.0                    0         32768 ?
Router# show bgp process                  
Mon Jul  9 16:47:39.428 PDT

BGP Process Information: 
...
Use origin-AS validity in bestpath decisions
Allow (origin-AS) INVALID paths
Signal origin-AS validity state to neighbors

Address family: IPv4 Unicast
...
Origin-AS validation is enabled for this address-family
Use origin-AS validity in bestpath decisions for this address-family
Allow (origin-AS) INVALID paths for this address-family
Signal origin-AS validity state to neighbors with this address-family

Configure RPKI Bestpath Computation

Perform this task to configure RPKI bestpath computation options.

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:
RP/0/RP0/CPU0:router(config)#router bgp 100

Specifies the BGP AS number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

rpki bestpath use origin-as validity

Example:
RP/0/RP0/CPU0:router(config-bgp)#bgp bestpath origin-as use validity

Enables the validity states of BGP paths to affect the path's preference in the BGP bestpath process. This configuration can also be done in router BGP address family submode.

Step 4

rpki bestpath origin-as allow invalid

Example:
RP/0/RP0/CPU0:router(config-bgp)#bgp bestpath origin-as allow invalid

Allows all "invalid" paths to be considered for BGP bestpath computation.

Note

 

This configuration can also be done at global address family, neighbor, and neighbor address family submodes. Configuring rpki bestpath origin-as allow invalid in router BGP and address family submodes allow all "invalid" paths to be considered for BGP bestpath computation. By default, all such paths are not bestpath candidates. Configuring pki bestpath origin-as allow invalid in neighbor and neighbor address family submodes allow all "invalid" paths from that specific neighbor or neighbor address family to be considered as bestpath candidates. The neighbor must be an eBGP neighbor.

This configuration takes effect only when the rpki bestpath use origin-as validity configuration is enabled.

Step 5

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Resilient Per-CE Label Allocation Mode

The Resilient Per-CE Label Allocation is an extension of the Per-CE label allocation mode to support Prefix Independent Convergence (PIC) and load balancing. At present, the three label allocation modes, Per-Prefix, Per-CE, and Per-VRF have these restrictions:
  • No support for load balancing across CEs

  • Temporary forwarding loop during local traffic diversion to support PIC

  • No support for EIBGP multipath load balancing

  • Forwarding performance impact

In the Resilient Per-CE label allocation scheme, BGP installs a unique rewrite label in LSD for every unique set of CE paths or next hops. There may be one or more prefixes in BGP table that points to this label. BGP also installs the CE paths (primary) and optionally a backup PE path into RIB. FIB learns about the label rewrite information from LSD and the IP paths from RIB. In steady state, labeled traffic destined to the resilient per-CE label is load balanced across all the CE next hops. When all the CE paths fail, any traffic destined to that label will result in an IP lookup and will be forwarded towards the backup PE path, if available. This action is performed on the label independently of the number of prefixes that may point to the label, resulting in the PIC behavior during primary paths failure.

Configure Resilient Per-CE Label Allocation Mode Under VRF Address Family

Perform this task to configure resilient per-ce label allocation mode under VRF address family.

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure
RP/0/RP0/CPU0:router(config)#

Enters global configuration mode.

Step 2

router bgpas-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 666
RP/0/RP0/CPU0:router(config-bgp)#

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

vrfvrf-instance

Example:

RP/0/RP0/CPU0:router(config-bgp)# vrf vrf-pe
RP/0/RP0/CPU0:router(config-bgp-vrf)#

Configures a VRF instance.

Step 4

address-family {ipv4 | ipv6} unicast

Example:

RP/0/RP0/CPU0:router(config-bgp-vrf)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-vrf-af)#

Specifies either an IPv4 or IPv6 address family unicast and enters address family configuration submode.

Step 5

label-mode per-ce

Example:

RP/0/RP0/CPU0:router(config-bgp-vrf-af)# label mode per-ce
RP/0/RP0/CPU0:router(config-bgp-vrf-af)#

Configures resilient per-ce label allocation mode.

Step 6

Do one of the following:

  • end
  • commit
Example:

RP/0/RP0/CPU0:router(config-bgp-vrf-af)# end

or


RP/0/RP0/CPU0:router(config-bgp-vrf-af)# commit

Saves configuration changes.

  • When you issue the end command, the system prompts you to commit changes:

    
      Uncommitted changes found, commit them before exiting(yes/no/cancel)?[cancel]:
    • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

    • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

    • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

  • Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.


This example shows how to configure resilient per-ce label allocation mode under VRF address family:


RP/0/RP0/CPU0:router# configure
RP/0/RP0/CPU0:router(config)# router bgp 666
RP/0/RP0/CPU0:router(config-bgp)# vrf vrf-pe
RP/0/RP0/CPU0:router(config-bgp-vrf)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-bgp-vrf-af)# label mode per-ce
RP/0/RP0/CPU0:router(config-bgp-vrf-af)# end

Configure Resilient Per-CE Label Allocation Mode Using Route-Policy

Perform this task to configure resilient per-ce label allocation mode using a route-policy.

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure
RP/0/RP0/CPU0:router(config)#

Enters global configuration mode.

Step 2

route-policypolicy-name

Example:

RP/0/RP0/CPU0:router(config)# route-policy route1
RP/0/RP0/CPU0:router(config-rpl)#

Creates a route policy and enters route policy configuration mode.

Step 3

set label-mode per-ce

Example:

RP/0/RP0/CPU0:router(config-rpl)# set label-mode per-ce
RP/0/RP0/CPU0:router(config-rpl)#

Configures resilient per-ce label allocation mode.

Step 4

Do one of the following:

  • end
  • commit
Example:

RP/0/RP0/CPU0:router(config-rpl)# end

or


RP/0/RP0/CPU0:router(config-rpl)# commit

Saves configuration changes.

  • When you issue the end command, the system prompts you to commit changes:

    
      Uncommitted changes found, commit them before exiting(yes/no/cancel)?[cancel]:
    • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

    • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

    • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

  • Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.


This example shows how to configure resilient per-ce label allocation mode using a route-policy:


RP/0/RP0/CPU0:router# configure
RP/0/RP0/CPU0:router(config)# route-policy route1
RP/0/RP0/CPU0:router(config-rpl)# set label-mode per-ce
RP/0/RP0/CPU0:router(config-rpl)# end

This example shows how to configure route-policy to vrf :

RP/0/RP0/CPU0:(config)# router bgp 666                
RP/0/RP0/CPU0:(config-bgp)# vrf vrf-pe
RP/0/RP0/CPU0:(config-bgp-vrf)# address-family ipv4 unicast
RP/0/RP0/CPU0:(config-bgp-vrf-af)# label mode route-policy route1

BGP VRF Dynamic Route Leaking

The Border Gateway Protocol (BGP) dynamic route leaking feature provides the ability to import routes between the default-vrf (Global VRF) and any other non-default VRF, to provide connectivity between a global and a VPN host. The import process installs the Internet route in a VRF table or a VRF route in the Internet table, providing connectivity.

The dynamic route leaking is enabled by:

  • Importing from default-VRF to non-default-VRF, using the import from default-vrf route-policy route-policy-name [ advertise-as-vpn] command in VRF address-family configuration mode.

    If the advertise-as-vpn option is configured, the paths imported from the default-VRF to the non-default-VRF are advertised to the PEs as well as to the CEs. If the advertise-as-vpn option is not configured, the paths imported from the default-VRF to the non-default-VRF are not advertised to the PE. However, the paths are still advertised to the CEs.

  • Importing from non-default-VRF to default VRF, using the export to default-vrf route-policy route-policy-name command in VRF address-family configuration mode.

A route-policy is mandatory to filter the imported routes. This reduces the risk of unintended import of routes between the Internet table and the VRF tables and the corresponding security issues. There is no hard limit on the number of prefixes that can be imported. The import creates a new prefix in the destination VRF, which increases the total number of prefixes and paths. However, each VRF importing global routes adds workload equivalent to a neighbor receiving the global table. This is true even if the user filters out all but a few prefixes. Hence, importing five to ten VRFs is ideal.

Configure VRF Dynamic Route Leaking

Perform these steps to import routes from default-VRF to non-default VRF or to import routes from non-default VRF to default VRF.
Before you begin

A route-policy is mandatory for configuring dynamic route leaking. Use the route-policy route-policy-name command in global configuration mode to configure a route-policy.

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

vrf vrf_name

Example:
RP/0/RSP0/CPU0:PE51_ASR-9010(config)#vrf vrf_1

Enters VRF configuration mode.

Step 3

address-family {ipv4 | ipv6} unicast

Example:
RP/0/RP0/CPU0:router(config-vrf)#address-family ipv6 unicast

Enters VRF address-family configuration mode.

Step 4

Use one of these options:

  • import from default-vrf route-policy route-policy-name [ advertise-as-vpn]
  • export to default-vrf route-policy route-policy-name
Example:
RP/0/RP0/CPU0:router(config-vrf-af)#import from default-vrf route-policy rpl_dynamic_route_import

or

RP/0/RP0/CPU0:router(config-vrf-af)#export to default-vrf route-policy rpl_dynamic_route_export
Imports routes from default-VRF to non-default VRF or from non-default VRF to default-VRF.
  • import from default-vrf —configures import from default-VRF to non-default-VRF.

    If the advertise-as-vpn option is configured, the paths imported from the default-VRF to the non-default-VRF are advertised to the PEs as well as to the CEs. If the advertise-as-vpn option is not configured, the paths imported from the default-VRF to the non-default-VRF are not advertised to the PE. However, the paths are still advertised to the CEs.

  • export to default-vrf —configures import from non-default-VRF to default VRF. The paths imported from the default-VRF are advertised to other PEs.

Step 5

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


VRF Dynamic Route Leaking Configuration: Example
Import Routes from default-VRF to non-default-VRF:

vrf vrf_1
 address-family ipv6 unicast
  import from default-vrf route-policy rpl_dynamic_route_import
 !
end
Import Routes from non-default-VRF to default-VRF

vrf vrf_1
 address-family ipv6 unicast
    export to default-vrf route-policy rpl_dynamic_route_export
 !
end
What to do next

These show bgp command output displays information from the dynamic route leaking configuration:

  • Use the show bgp prefix command to display the source-RD and the source-VRF for imported paths, including the cases when IPv4 or IPv6 unicast prefixes have imported paths.

  • Use the show bgp imported-routes command to display IPv4 unicast and IPv6 unicast address-families under the default-VRF.

Configuring a VPN Routing and Forwarding Instance in BGP

Layer 3 (virtual private network) VPN can be configured only if there is an available Layer 3 VPN license for the line card slot on which the feature is being configured. If advanced IP license is enabled, 4096 Layer 3 VPN routing and forwarding instances (VRFs) can be configured on an interface. If the infrastructure VRF license is enabled, eight Layer 3 VRFs can be configured on the line card.

The following error message appears if the appropriate licence is not enabled:
RP/0/RP0/CPU0:router#LC/0/0/CPU0:Dec 15 17:57:53.653 : rsi_agent[247]:
%LICENSE-ASR9K_LICENSE-2-INFRA_VRF_NEEDED : 5 VRF(s) are configured without license A9K-iVRF-LIC in violation of the Software Right To Use Agreement. 
This feature may be disabled by the system without the appropriate license.
Contact Cisco to purchase the license immediately to avoid potential service interruption.

Note


An AIP license is not required for configuring L2VPN services.


The following tasks are used to configure a VPN routing and forwarding (VRF) instance in BGP:

Define Virtual Routing and Forwarding Tables in Provider Edge Routers

Perform this task to define the VPN routing and forwarding (VRF) tables in the provider edge (PE) routers.

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

vrf vrf-name

Example:

RP/0/RP0/CPU0:router(config)# vrf vrf_pe

Configures a VRF instance.

Step 3

address-family { ipv4 | ipv6 } unicast

Example:

RP/0/RP0/CPU0:router(config-vrf)# address-family ipv4 unicast

Specifies either the IPv4 or IPv6 address family and enters address family configuration submode.

To see a list of all the possible keywords and arguments for this command, use the CLI help (?).

Step 4

maximum prefix maximum [ threshold ]

Example:

RP/0/RP0/CPU0:router(config-vrf-af)# maximum prefix 2300

Configures a limit to the number of prefixes allowed in a VRF table.

A maximum number of routes is applicable to dynamic routing protocols as well as static or connected routes.

You can specify a threshold percentage of the prefix limit using the mid-threshold argument.

Step 5

import route-policy policy-name

Example:

RP/0/RP0/CPU0:router(config-vrf-af)# import route-policy policy_a

(Optional) Provides finer control over what gets imported into a VRF. This import filter discards prefixes that do not match the specified policy-name argument.

Step 6

import route-target [ as-number : nn | ip-address : nn ]

Example:

RP/0/RP0/CPU0:router(config-vrf-af)# import route-target 234:222

Specifies a list of route target (RT) extended communities. Only prefixes that are associated with the specified import route target extended communities are imported into the VRF.

Step 7

export route-policy policy-name

Example:

RP/0/RP0/CPU0:router(config-vrf-af)# export route-policy policy_b

(Optional) Provides finer control over what gets exported into a VRF. This export filter discards prefixes that do not match the specified policy-name argument.

Step 8

export route-target [ as-number : nn | ip-address : nn ]

Example:

RP/0/RP0/CPU0:routerr(config-vrf-af)# export route-target 123:234

Specifies a list of route target extended communities. Export route target communities are associated with prefixes when they are advertised to remote PEs. The remote PEs import them into VRFs which have import RTs that match these exported route target communities.

Step 9

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Configure Route Distinguisher

The route distinguisher (RD) makes prefixes unique across multiple VPN routing and forwarding (VRF) instances.

In the L3VPN multipath same route distinguisher (RD)environment, the determination of whether to install a prefix in RIB or not is based on the prefix's bestpath. In a rare misconfiguration situation, where the best pah is not a valid path to be installed in RIB, BGP drops the prefix and does not consider the other paths. The behavior is different for different RD setup, where the non-best multipath will be installed if the best multipath is invalid to be installed in RIB.

Perform this task to configure the RD.

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 120

Enters BGP configuration mode allowing you to configure the BGP routing process.

Step 3

bgp router-id ip-address

Example:

RP/0/RP0/CPU0:router(config-bgp)# bgp router-id 10.0.0.0

Configures a fixed router ID for the BGP-speaking router.

Step 4

vrf vrf-name

Example:

RP/0/RP0/CPU0:router(config-bgp)# vrf vrf_pe

Configures a VRF instance.

Step 5

rd { as-number : nn | ip-address : nn | auto }

Example:

RP/0/RP0/CPU0:router(config-bgp-vrf)# rd 345:567

Configures the route distinguisher.

Use the auto keyword if you want the router to automatically assign a unique RD to the VRF.

Automatic assignment of RDs is possible only if a router ID is configured using the bgp router-id command in router configuration mode. This allows you to configure a globally unique router ID that can be used for automatic RD generation. The router ID for the VRF does not need to be globally unique, and using the VRF router ID would be incorrect for automatic RD generation. Having a single router ID also helps in checkpointing RD information for BGP graceful restart, because it is expected to be stable across reboots.

Step 6

Do one of the following:

  • end
  • commit
Example:

RP/0/RP0/CPU0:router(config-bgp-vrf)# end

or


RP/0/RP0/CPU0:router(config-bgp-vrf)# commit

Saves configuration changes.

  • When you issue the end command, the system prompts you to commit changes:

    
      Uncommitted changes found, commit them before exiting(yes/no/cancel)?[cancel]:
    
    • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to XR EXEC mode.

    • Entering no exits the configuration session and returns the router to XR EXEC mode without committing the configuration changes.

    • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

  • Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.


Configure PE-PE or PE-RR Interior BGP Sessions

To enable BGP to carry VPN reachability information between provider edge (PE) routers you must configure the PE-PE interior BGP (iBGP) sessions. A PE uses VPN information carried from the remote PE router to determine VPN connectivity and the label value to be used so the remote (egress) router can demultiplex the packet to the correct VPN during packet forwarding.

The PE-PE, PE-route reflector (RR) iBGP sessions are defined to all PE and RR routers that participate in the VPNs configured in the PE router.

Perform this task to configure PE-PE iBGP sessions and to configure global VPN options on a PE.

Procedure

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

address-family vpnv4 unicast

Example:

RP/0/RP0/CPU0:router(config-bgp)# address-family vpvn4 unicast

Enters VPN address family configuration mode.

Step 4

exit

Example:

RP/0/RP0/CPU0:router(config-bgp-af)# exit

Exits the current configuration mode.

Step 5

neighbor ip-address

Example:

RP/0/RP0/CPU0:router(config-bgp)# neighbor 172.16.1.1

Configures a PE iBGP neighbor.

Step 6

remote-as as-number

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 1

Assigns the neighbor a remote autonomous system number.

Step 7

description text

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# description neighbor 172.16.1.1

(Optional) Provides a description of the neighbor. The description is used to save comments and does not affect software function.

Step 8

password { clear | encrypted } password

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# password encrypted 123abc

Enables Message Digest 5 (MD5) authentication on the TCP connection between the two BGP neighbors.

Step 9

shutdown

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# shutdown

Terminates any active sessions for the specified neighbor and removes all associated routing information.

Step 10

timers keepalive hold-time

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# timers 12000 200

Set the timers for the BGP neighbor.

Step 11

update-source type interface-id

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# update-source gigabitEthernet 0/1/5/0

Allows iBGP sessions to use the primary IP address from a specific interface as the local address when forming an iBGP session with a neighbor.

Step 12

address-family vpnv4 unicast

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family vpvn4 unicast

Enters VPN neighbor address family configuration mode.

Step 13

route-policy route-policy-name in

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr-af)# route-policy pe-pe-vpn-in in

Specifies a routing policy for an inbound route. The policy can be used to filter routes or modify route attributes.

Step 14

route-policy route-policy-name out

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr-af)# route-policy pe-pe-vpn-out out

Specifies a routing policy for an outbound route. The policy can be used to filter routes or modify route attributes.

Step 15

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.


Configure BGP as PE-CE Protocol

Perform this task to configure BGP on the PE and establish PE-CE communication using BGP.

Procedure
  Command or Action Purpose

Step 1

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters mode.

Step 2

router bgp as-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 120

Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

vrf vrf-name

Example:

RP/0/RP0/CPU0:router(config-bgp)# vrf vrf_pe_2

Enables BGP routing for a particular VRF on the PE router.

Step 4

bgp router-id ip-address

Example:

RP/0/RP0/CPU0:router(config-bgp-vrf)# bgp router-id 172.16.9.9

Configures a fixed router ID for a BGP-speaking router.

Step 5

label-allocation-mode per-ce

Example:

RP/0/RP0/CPU0:router(config-bgp-vrf)# 
label-allocation-mode per-ce
  • Configures The per-ce keyword configures the per-CE label allocation mode to avoid an extra lookup on the PE router and conserve label space (per-prefix is the default label allocation mode). In this mode, the PE router allocates one label for every immediate next-hop (in most cases, this would be a CE router). This label is directly mapped to the next hop, so there is no VRF route lookup performed during data forwarding. However, the number of labels allocated would be one for each CE rather than one for each VRF. Because BGP knows all the next hops, it assigns a label for each next hop (not for each PE-CE interface). When the outgoing interface is a multiaccess interface and the media access control (MAC) address of the neighbor is not known, Address Resolution Protocol (ARP) is triggered during packet forwarding.

  • The per-vrf keyword configures the same label to be used for all the routes advertised from a unique VRF.

Step 6

address-family { ipv4 | ipv6 } unicast

Example:

RP/0/RP0/CPU0:router(config-vrf)# address-family ipv4 unicast

Specifies either an IPv4 or IPv6 address family unicast and enters address family configuration submode.

To see a list of all the possible keywords and arguments for this command, use the CLI help (?).

Step 7

network { ip-address / prefix-length | ip-address mask }

Example:

RP/0/RP0/CPU0:router(config-bgp-vrf-af)# network 172.16.5.5
               

Originates a network prefix in the address family table in the VRF context.

Step 8

aggregate-address address / mask-length

Example:

RP/0/RP0/CPU0:router(config-bgp-vrf-af)# aggregate-address 10.0.0.0/24

Configures aggregation in the VRF address family context to summarize routing information to reduce the state maintained in the core. This summarization introduces some inefficiency in the PE edge, because an additional lookup is required to determine the ultimate next hop for a packet. When configured, a summary prefix is advertised instead of a set of component prefixes, which are more specifics of the aggregate. The PE advertises only one label for the aggregate. Because component prefixes could have different next hops to CEs, an additional lookup has to be performed during data forwarding.

Step 9

exit

Example:

RP/0/RP0/CPU0:router(config-bgp-vrf-af)# exit

Exits the current configuration mode.

Step 10

neighbor ip-address

Example:

RP/0/RP0/CPU0:router(config-bgp-vrf)# neighbor 10.0.0.0

Configures a CE neighbor. The ip-address argument must be a private address.

Step 11

remote-as as-number

Example:

RP/0/RP0/CPU0:router(config-bgp-vrf-nbr)# remote-as 2

Configures the remote AS for the CE neighbor.

Step 12

password { clear | encrypted } password

Example:

RP/0/RP0/CPU0:router(config-bgp-vrf-nbr)# password encrypted 234xyz

Enable Message Digest 5 (MD5) authentication on a TCP connection between two BGP neighbors.

Step 13

ebgp-multihop [ ttl-value ]

Example:

RP/0/RP0/CPU0:router(config-bgp-vrf-nbr)# ebgp-multihop 55

Configures the CE neighbor to accept and attempt BGP connections to external peers residing on networks that are not directly connected.

Step 14

Do one of the following:

  • address-family { ipv4 | ipv6 } unicast
  • address-family {ipv4 {unicast | labeled-unicast} | ipv6 unicast}
Example:

RP/0/RP0/CPU0:router(config-vrf)# 
address-family ipv4 unicast

Specifies either an IPv4 or IPv6 address family unicast and enters address family configuration submode.

To see a list of all the possible keywords and arguments for this command, use the CLI help (?).

Step 15

site-of-origin [ as-number : nn | ip-address : nn ]

Example:

RP/0/RP0/CPU0:router(config-bgp-vrf-nbr-af)# site-of-origin 234:111

Configures the site-of-origin (SoO) extended community. Routes that are learned from this CE neighbor are tagged with the SoO extended community before being advertised to the rest of the PEs. SoO is frequently used to detect loops when as-override is configured on the PE router. If the prefix is looped back to the same site, the PE detects this and does not send the update to the CE.

Step 16

as-override

Example:

RP/0/RP0/CPU0:router(config-bgp-vrf-nbr-af)# as-override

Configures AS override on the PE router. This causes the PE router to replace the CE’s ASN with its own (PE) ASN.

Note

 

This loss of information could lead to routing loops; to avoid loops caused by as-override, use it in conjunction with site-of-origin.

Step 17

allowas-in [ as-occurrence-number ]

Example:

RP/0/RP0/CPU0:router(config-bgp-vrf-nbr-af)# allowas-in 5

Allows an AS path with the PE autonomous system number (ASN) a specified number of times.

Hub and spoke VPN networks need the looping back of routing information to the HUB PE through the HUB CE. When this happens, due to the presence of the PE ASN, the looped-back information is dropped by the HUB PE. To avoid this, use the allowas-in command to allow prefixes even if they have the PEs ASN up to the specified number of times.

Step 18

route-policy route-policy-name in

Example:

RP/0/RP0/CPU0:router(config-bgp-vrf-nbr-af)# route-policy pe_ce_in_policy in

Specifies a routing policy for an inbound route. The policy can be used to filter routes or modify route attributes.

Step 19

route-policy route-policy-name out

Example:

RP/0/RP0/CPU0:router(config-bgp-vrf-nbr-af)# route-policy pe_ce_out_policy out

Specifies a routing policy for an outbound route. The policy can be used to filter routes or modify route attributes.

Step 20

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:
  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.

Resetting an eBGP Session Immediately Upon Link Failure

By default, if a link goes down, all BGP sessions of any directly adjacent external peers are immediately reset. Use the bgp fast-external-fallover disable command to disable automatic resetting. Turn the automatic reset back on using the no bgp fast-external-fallover disable command.

eBGP sessions flap when the node reaches 3500 eBGP sessions with BGP timer values set as 10 and 30. To support more than 3500 eBGP sessions, increase the packet rate by using the lpts pifib hardware police location location-id command. Following is a sample configuration to increase the eBGP sessions:
RP/0/RP0/CPU0:router#configure 
RP/0/RP0/CPU0:router(config)#lpts pifib hardware police location 0/2/CPU0
RP/0/RP0/CPU0:router(config-pifib-policer-per-node)#flow bgp configured rate 4000
RP/0/RP0/CPU0:router(config-pifib-policer-per-node)#flow bgp known rate 4000
RP/0/RP0/CPU0:router(config-pifib-policer-per-node)#flow bgp default rate 4000
RP/0/RP0/CPU0:router(config-pifib-policer-per-node)#commit

Information about Implementing BGP

To implement BGP, you need to understand the following concepts:

BGP Router Identifier

For BGP sessions between neighbors to be established, BGP must be assigned a router ID. The router ID is sent to BGP peers in the OPEN message when a BGP session is established.

BGP attempts to obtain a router ID in the following ways (in order of preference):

  • By means of the address configured using the bgp router-id command in router configuration mode.

  • By using the highest IPv4 address on a loopback interface in the system if the router is booted with saved loopback address configuration.

  • By using the primary IPv4 address of the first loopback address that gets configured if there are not any in the saved configuration.

If none of these methods for obtaining a router ID succeeds, BGP does not have a router ID and cannot establish any peering sessions with BGP neighbors. In such an instance, an error message is entered in the system log, and the show bgp summary command displays a router ID of 0.0.0.0. After BGP has obtained a router ID, it continues to use it even if a better router ID becomes available. This usage avoids unnecessary flapping for all BGP sessions. However, if the router ID currently in use becomes invalid (because the interface goes down or its configuration is changed), BGP selects a new router ID (using the rules described) and all established peering sessions are reset.


Note


We strongly recommend that the bgp router-id command is configured to prevent unnecessary changes to the router ID (and consequent flapping of BGP sessions).


BGP Default Limits

BGP imposes maximum limits on the number of neighbors that can be configured on the router and on the maximum number of prefixes that are accepted from a peer for a given address family. This limitation safeguards the router from resource depletion caused by misconfiguration, either locally or on the remote neighbor. The following limits apply to BGP configurations:

  • The default maximum number of peers that can be configured is 4000. The default can be changed using the bgp maximum neighbor command. The limit range is 1–15000. Any attempt to configure additional peers beyond the maximum limit or set the maximum limit to a number that is less than the number of peers that are currently configured will fail.

  • To prevent a peer from flooding BGP with advertisements, a limit is placed on the number of prefixes that are accepted from a peer for each supported address family. The default limits can be overridden through configuration of the maximum-prefix limit command for the peer for the appropriate address family. The following default limits are used if the user does not configure the maximum number of prefixes for the address family:
    • 512K (524,288) prefixes for IPv4 unicast

    • 128K (131,072) prefixes for IPv6 unicast

    • 512K (524,288) prefixes for VPNv4 unicast

    A cease notification message is sent to the neighbor and the peering with the neighbor is terminated when the number of prefixes that are received from the peer for a given address family exceeds the maximum limit (either set by default or configured by the user) for that address family.

    It is possible that the maximum number of prefixes for a neighbor for a given address family has been configured after the peering with the neighbor has been established and some prefixes have already been received from the neighbor for that address family. A cease notification message is sent to the neighbor and peering with the neighbor is terminated immediately after the configuration if the configured maximum number of prefixes is fewer than the number of prefixes that have already been received from the neighbor for the address family.

BGP Attributes and Operators

This table summarizes the BGP attributes and operators per attach points.

Table 3. BGP Attributes and Operators

Attach Point

Attribute

Match

Set

aggregation

as-path

in

is-local

length

neighbor-is

originates-from

passes-through

unique-length

as-path-length

is, ge, le, eq

as-path-unique-length

is, ge, le, eq

community

is-empty

matches-any

matches-every

set

set additive

delete in

delete not in

delete all

destination

in

extcommunity cost

set

set additive

local-preference

is, ge, le, eq

set

med

is, eg, ge, le

setset +set -

next-hop

in

set

origin

is

set

source

in

suppress-route

suppress-route

weight

set

allocate-label

as-path

in

is-local

length

neighbor-is

originates-from

passes-through

unique-length

as-path-length

is, ge, le, eq

as-path-unique-length

is, ge, le, eq

community

is-empty

matches-any

matches-every

destination

in

label

set

local-preference

is, ge, le, eq

med

is, eg, ge, le

next-hop

in

origin

is

source

in

clear-policy

as-path

in

is-local

length

neighbor-is

originates-from

passes-through

unique-length

as-path-length

is, ge, le, eq

as-path-unique-length

is, ge, le, eq

dampening

as-path

in

is-local

length

neighbor-is

originates-from

passes-through

unique-length

as-path-length

is, ge, le, eq

as-path-unique-length

is, ge, le, eq

community

is-empty

matches-any

matches-every

dampening

—/

set dampening

destination

in

local-preference

is, ge, le, eq

med

is, eg, ge, le

next-hop

in

origin

is

source

in

debug

destination

in

default originate

med

set

set +

set -

rib-has-route

in

neighbor-in

as-path

in

is-local

length

NA

neighbor-is

originates-from

passes-through

unique-length

prepend

prepend most-recent

remove as-path private-as

replace

as-path-length

is, ge, le, eq

as-path-unique-length

is, ge, le, eq

communitycommunity with ‘peeras’

is-empty

matches-any

matches-every

set

set additive

delete-in

delete-not-in

delete-all

destination

in

extcommunity cost

set

set additive

extcommunity rt

is-empty

matches-any

matches-every

matches-within

set

additive

delete-in

delete-not-in

delete-all

extcommunity soo

is-empty

matches-any

matches-every

matches-within

local-preference

is, ge, le, eq

set

med

is, eg, ge, le

set

set +

set -

next-hop

in

set

set peer address

origin

is

set

route-aggregated

route-aggregated

NA

source

in

weight

set

neighbor-out

as-path

in

is-local

length

neighbor-is

originates-from

passes-through

unique-length

prepend

prepend most-recent

remove as-path private-as

replace

as-path-length

is, ge, le, eq

as-path-unique-length

is, ge, le, eq

communitycommunity with ‘peeras’

is-empty

matches-any

matches-every

set

set additive

delete-in

delete-not-in

delete-all

destination

in

extcommunity cost

set

set additive

extcommunity rt

is-empty

matches-any

matches-every

matches-within

set

additive

delete-in

delete-not-in

delete-all

extcommunity soo

is-empty

matches-any

matches-every

matches-within

local-preference

is, ge, le, eq

set

med

is, eg, ge, le

set

set +

set -

set max-unreachable

set igp-cost

next-hop

in

set

set self

origin

is

set

path-type

is

rd

in

route-aggregated

route-aggregated

source

in

unsuppress-route

unsuppress-route

vpn-distinguisher

set

neighbor-orf

orf-prefix

in

n/a

network

as-path

prepend

community

set

set additive

delete-in

delete-not-in

delete-all

destination

in

extcommunity cost

set

set additive

mpls-label

route-has-label

local-preference

set

med

set

set+

set-

next-hop

in

set

origin

set

route-type

is

tag

is, ge, le, eq

weight

set

next-hop

destination

in

protocol

is,in

source

in

redistribute

as-path

prepend

community

set

set additive

delete in

delete not in

delete all

destination

in

extcommunity cost

setset additive

local-preference

set

med

set

set+

set-

next-hop

in

set

origin

set

mpls-label

route-has-label

route-type

is

tag

is, eq, ge, le

weight

set

retain-rt

extcommunity rt

is-empty

matches-any

matches-every

matches-within

show

as-path

in

is-local

length

neighbor-is

originates-from

passes-through

unique-length

as-path-length

is, ge, le, eq

as-path-unique-length

is, ge, le, eq

community

is-empty

matches-any

matches-every

destination

in

extcommunity rt

is-empty

matches-any

matches-every

matches-within

extcommunity soo

is-empty

matches-any

matches-every

matches-within

med

is, eg, ge, le

next-hop

in

origin

is

source

in

Some BGP route attributes are inaccessible from some BGP attach points for various reasons. For example, the set med igp-cost only command makes sense when there is a configured igp-cost to provide a source value.

This table summarizes which operations are valid and where they are valid.

Table 4. Restricted BGP Operations by Attach Point

Command

import

export

aggregation

redistribution

prepend as-path most-recent

eBGP only

eBGP only

n/a

n/a

replace as-path

eBGP only

eBGP only

n/a

n/a

set med igp-cost

forbidden

eBGP only

forbidden

forbidden

set weight

n/a

forbidden

n/a

n/a

suppress

forbidden

forbidden

n/a

forbidden

BGP Best Path Algorithm

BGP routers typically receive multiple paths to the same destination. The BGP best-path algorithm determines the best path to install in the IP routing table and to use for forwarding traffic. This section describes the Cisco IOS XR software implementation of BGP best-path algorithm, as specified in Section 9.1 of the Internet Engineering Task Force (IETF) Network Working Group draft-ietf-idr-bgp4-24.txt document.

The BGP best-path algorithm implementation is in three parts:

  • Part 1—Compares two paths to determine which is better.

  • Part 2—Iterates over all paths and determines which order to compare the paths to select the overall best path.

  • Part 3—Determines whether the old and new best paths differ enough so that the new best path should be used.


Note


The order of comparison determined by Part 2 is important because the comparison operation is not transitive; that is, if three paths, A, B, and C exist, such that when A and B are compared, A is better, and when B and C are compared, B is better, it is not necessarily the case that when A and C are compared, A is better. This nontransitivity arises because the multi exit discriminator (MED) is compared only among paths from the same neighboring autonomous system (AS) and not among all paths.


Comparing Pairs of Paths

Perform the following steps to compare two paths and determine the better path:

  1. If either path is invalid (for example, a path has the maximum possible MED value or it has an unreachable next hop), then the other path is chosen (provided that the path is valid).

  2. If the paths have unequal pre-bestpath cost communities, the path with the lower pre-bestpath cost community is selected as the best path.

  3. If the paths have unequal weights, the path with the highest weight is chosen.

    Note


    The weight is entirely local to the router, and can be set with the weight command or using a routing policy.


  4. If the paths have unequal local preferences, the path with the higher local preference is chosen.


    Note


    If a local preference attribute was received with the path or was set by a routing policy, then that value is used in this comparison. Otherwise, the default local preference value of 100 is used. The default value can be changed using the bgp default local-preference command.


  5. If one of the paths is a redistributed path, which results from a redistribute or network command, then it is chosen. Otherwise, if one of the paths is a locally generated aggregate, which results from an aggregate-address command, it is chosen.


    Note


    Step 1 through Step 4 implement the “Path Selection with BGP”of RFC 1268.


  6. If the paths have unequal AS path lengths, the path with the shorter AS path is chosen. This step is skipped if bgp bestpath as-path ignore command is configured.


    Note


    When calculating the length of the AS path, confederation segments are ignored, and AS sets count as 1.



    Note


    eiBGP specifies internal and external BGP multipath peers. eiBGP allows simultaneous use of internal and external paths.


  7. If the paths have different origins, the path with the lower origin is selected. Interior Gateway Protocol (IGP) is considered lower than EGP, which is considered lower than INCOMPLETE.

  8. If appropriate, the MED of the paths is compared. If they are unequal, the path with the lower MED is chosen.

    A number of configuration options exist that affect whether or not this step is performed. In general, the MED is compared if both paths were received from neighbors in the same AS; otherwise the MED comparison is skipped. However, this behavior is modified by certain configuration options, and there are also some corner cases to consider.

    If the bgp bestpath med always command is configured, then the MED comparison is always performed, regardless of neighbor AS in the paths. Otherwise, MED comparison depends on the AS paths of the two paths being compared, as follows:

    • If a path has no AS path or the AS path starts with an AS_SET, then the path is considered to be internal, and the MED is compared with other internal paths.

    • If the AS path starts with an AS_SEQUENCE, then the neighbor AS is the first AS number in the sequence, and the MED is compared with other paths that have the same neighbor AS.

    • If the AS path contains only confederation segments or starts with confederation segments followed by an AS_SET, then the MED is not compared with any other path unless the bgp bestpath med confed command is configured. In that case, the path is considered internal and the MED is compared with other internal paths.

    • If the AS path starts with confederation segments followed by an AS_SEQUENCE, then the neighbor AS is the first AS number in the AS_SEQUENCE, and the MED is compared with other paths that have the same neighbor AS.


    Note


    If no MED attribute was received with the path, then the MED is considered to be 0 unless the bgp bestpath med missing-as-worst command is configured. In that case, if no MED attribute was received, the MED is considered to be the highest possible value.


  9. If one path is received from an external peer and the other is received from an internal (or confederation) peer, the path from the external peer is chosen.

  10. If the paths have different IGP metrics to their next hops, the path with the lower IGP metric is chosen.

  11. If the paths have unequal IP cost communities, the path with the lower IP cost community is selected as the best path.

  12. If all path parameters in Step 1 through Step 10 are the same, then the router IDs are compared. If the path was received with an originator attribute, then that is used as the router ID to compare; otherwise, the router ID of the neighbor from which the path was received is used. If the paths have different router IDs, the path with the lower router ID is chosen.


    Note


    Where the originator is used as the router ID, it is possible to have two paths with the same router ID. It is also possible to have two BGP sessions with the same peer router, and therefore receive two paths with the same router ID.


  13. If the paths have different cluster lengths, the path with the shorter cluster length is selected. If a path was not received with a cluster list attribute, it is considered to have a cluster length of 0.

  14. Finally, the path received from the neighbor with the lower IP address is chosen. Locally generated paths (for example, redistributed paths) are considered to have a neighbor IP address of 0.

Order of Comparisons

The second part of the BGP best-path algorithm implementation determines the order in which the paths should be compared. The order of comparison is determined as follows:

  1. The paths are partitioned into groups such that within each group the MED can be compared among all paths. The same rules as in are used to determine whether MED can be compared between any two paths. Normally, this comparison results in one group for each neighbor AS. If the bgp bestpath med always command is configured, then there is just one group containing all the paths.

  2. The best path in each group is determined. Determining the best path is achieved by iterating through all paths in the group and keeping track of the best one seen so far. Each path is compared with the best-so-far, and if it is better, it becomes the new best-so-far and is compared with the next path in the group.

  3. A set of paths is formed containing the best path selected from each group in Step 2. The overall best path is selected from this set of paths, by iterating through them as in Step 2.

Best Path Change Suppression

The third part of the implementation is to determine whether the best-path change can be suppressed or not—whether the new best path should be used, or continue using the existing best path. The existing best path can continue to be used if the new one is identical to the point at which the best-path selection algorithm becomes arbitrary (if the router-id is the same). Continuing to use the existing best path can avoid churn in the network.


Note


This suppression behavior does not comply with the IETF Networking Working Group draft-ietf-idr-bgp4-24.txt document, but is specified in the IETF Networking Working Group draft-ietf-idr-avoid-transition-00.txt document.


The suppression behavior can be turned off by configuring the bgp bestpath compare-routerid command. If this command is configured, the new best path is always preferred to the existing one.

Otherwise, the following steps are used to determine whether the best-path change can be suppressed:

  1. If the existing best path is no longer valid, the change cannot be suppressed.

  2. If either the existing or new best paths were received from internal (or confederation) peers or were locally generated (for example, by redistribution), then the change cannot be suppressed. That is, suppression is possible only if both paths were received from external peers.

  3. If the paths were received from the same peer (the paths would have the same router-id), the change cannot be suppressed. The router ID is calculated using rules in .

  4. If the paths have different weights, local preferences, origins, or IGP metrics to their next hops, then the change cannot be suppressed. Note that all these values are calculated using the rules in .

  5. If the paths have different-length AS paths and the bgp bestpath as-path ignore command is not configured, then the change cannot be suppressed. Again, the AS path length is calculated using the rules in .

  6. If the MED of the paths can be compared and the MEDs are different, then the change cannot be suppressed. The decision as to whether the MEDs can be compared is exactly the same as the rules in , as is the calculation of the MED value.

  7. If all path parameters in Step 1 through Step 6 do not apply, the change can be suppressed.

BGP Update Generation and Update Groups

The BGP Update Groups feature separates BGP update generation from neighbor configuration. The BGP Update Groups feature introduces an algorithm that dynamically calculates BGP update group membership based on outbound routing policies. This feature does not require any configuration by the network operator. Update group-based message generation occurs automatically and independently.

BGP Update Group

When a change to the configuration occurs, the router automatically recalculates update group memberships and applies the changes.

For the best optimization of BGP update group generation, we recommend that the network operator keeps outbound routing policy the same for neighbors that have similar outbound policies. This feature contains commands for monitoring BGP update groups.

BGP Cost Community Reference

The cost community attribute is applied to internal routes by configuring the set extcommunity cost command in a route policy. The cost community set clause is configured with a cost community ID number (0–255) and cost community number (0–4294967295). The cost community number determines the preference for the path. The path with the lowest cost community number is preferred. Paths that are not specifically configured with the cost community number are assigned a default cost community number of 2147483647 (the midpoint between 0 and 4294967295) and evaluated by the best-path selection process accordingly. When two paths have been configured with the same cost community number, the path selection process prefers the path with the lowest cost community ID. The cost-extended community attribute is propagated to iBGP peers when extended community exchange is enabled.

The following commands include the route-policy keyword, which you can use to apply a route policy that is configured with the cost community set clause:

  • aggregate-address

  • redistribute

  • network

BGP Next Hop Reference

Event notifications from the RIB are classified as critical and noncritical. Notifications for critical and noncritical events are sent in separate batches. BGP is notified when any of the following events occurs:
  • Next hop becomes unreachable

  • Next hop becomes reachable

  • Fully recursed IGP metric to the next hop changes

  • First hop IP address or first hop interface change

  • Next hop becomes connected

  • Next hop becomes unconnected

  • Next hop becomes a local address

  • Next hop becomes a nonlocal address


Note


Reachability and recursed metric events trigger a best-path recalculation.


However, a noncritical event is sent along with the critical events if the noncritical event is pending and there is a request to read the critical events.
  • Critical events are related to the reachability (reachable and unreachable), connectivity (connected and unconnected), and locality (local and nonlocal) of the next hops. Notifications for these events are not delayed.

  • Noncritical events include only the IGP metric changes. These events are sent at an interval of 3 seconds. A metric change event is batched and sent 3 seconds after the last one was sent.

BGP is notified when any of the following events occurs:

  • Next hop becomes unreachable

  • Next hop becomes reachable

  • Fully recursed IGP metric to the next hop changes

  • First hop IP address or first hop interface change

  • Next hop becomes connected

  • Next hop becomes unconnected

  • Next hop becomes a local address

  • Next hop becomes a nonlocal address


Note


Reachability and recursed metric events trigger a best-path recalculation.


The next-hop trigger delay for critical and noncritical events can be configured to specify a minimum batching interval for critical and noncritical events using the nexthop trigger-delay command. The trigger delay is address family dependent.

The BGP next-hop tracking feature allows you to specify that BGP routes are resolved using only next hops whose routes have the following characteristics:

  • To avoid the aggregate routes, the prefix length must be greater than a specified value.

  • The source protocol must be from a selected list, ensuring that BGP routes are not used to resolve next hops that could lead to oscillation.

This route policy filtering is possible because RIB identifies the source protocol of route that resolved a next hop as well as the mask length associated with the route. The nexthop route-policy command is used to specify the route-policy.

Next Hop as the IPv6 Address of Peering Interface

BGP can carry IPv6 prefixes over an IPv4 session. The next hop for the IPv6 prefixes can be set through a nexthop policy. In the event that the policy is not configured, the nexthops are set as the IPv6 address of the peering interface (IPv6 neighbor interface or IPv6 update source interface, if any one of the interfaces is configured).

If the nexthop policy is not configured and neither the IPv6 neighbor interface nor the IPv6 update source interface is configured, the next hop is the IPv4 mapped IPv6 address.

Scoped IPv4/VPNv4 Table Walk

To determine which address family to process, a next-hop notification is received by first de-referencing the gateway context associated with the next hop, then looking into the gateway context to determine which address families are using the gateway context. The IPv4 unicast and VPNv4 unicast address families share the same gateway context, because they are registered with the IPv4 unicast table in the RIB. As a result, both the global IPv4 unicast table and the VPNv4 table are is processed when an IPv4 unicast next-hop notification is received from the RIB. A mask is maintained in the next hop, indicating if whether the next hop belongs to IPv4 unicast or VPNv4 unicast, or both. This scoped table walk localizes the processing in the appropriate address family table.

Reordered Address Family Processing

The software walks address family tables based on the numeric value of the address family. When a next-hop notification batch is received, the order of address family processing is reordered to the following order:

  • IPv4 tunnel

  • VPNv4 unicast

  • VPNv6 unicast

  • IPv4 labeled unicast

  • IPv4 unicast

  • IPv4 MDT

  • IPv6 unicast

  • IPv6 labeled unicast

  • IPv4 tunnel

  • VPNv4 unicast

  • IPv4 unicast

  • IPv6 unicast

New Thread for Next-Hop Processing

The critical-event thread in the spkr process handles only next-hop, Bidirectional Forwarding Detection (BFD), and fast-external-failover (FEF) notifications. This critical-event thread ensures that BGP convergence is not adversely impacted by other events that may take a significant amount of time.

show, clear, and debug Commands

The show bgp nexthops command provides statistical information about next-hop notifications, the amount of time spent in processing those notifications, and details about each next hop registered with the RIB. The clear bgp nexthop performance-statistics command ensures that the cumulative statistics associated with the processing part of the next-hop show command can be cleared to help in monitoring. The clear bgp nexthop registration command performs an asynchronous registration of the next hop with the RIB.

The debug bgp nexthop command displays information on next-hop processing. The out keyword provides debug information only about BGP registration of next hops with RIB. The in keyword displays debug information about next-hop notifications received from RIB. The out keyword displays debug information about next-hop notifications sent to the RIB.

BGP Nonstop Routing Reference

BGP NSR provides nonstop routing during the following events:

  • Route processor switchover

  • Process crash or process failure of BGP or TCP

    Note


    BGP NSR is enabled by default. Use the nsr disable command to turn off BGP NSR. The no nsr disable command can also be used to turn BGP NSR back on if it has been disabled.

    In case of process crash or process failure, NSR will be maintained only if nsr process-failures switchover command is configured. In the event of process failures of active instances, the nsr process-failures switchover configures failover as a recovery action and switches over to a standby route processor (RP) or a standby distributed route processor (DRP) thereby maintaining NSR. An example of the configuration command is RP/0/RSP0/CPU0:router(config) # nsr process-failures switchover

    The nsr process-failures switchover command maintains both the NSR and BGP sessions in the event of a BGP or TCP process crash. Without this configuration, BGP neighbor sessions flap in case of a BGP or TCP process crash. This configuration does not help if the BGP or TCP process is restarted in which case the BGP neighbors are expected to flap.

    When the l2vpn_mgr process is restarted, the NSR client (te-control) flaps between the Ready and Not Ready state. This is the expected behavior and there is no traffic loss.


During route processor switchover and In-Service System Upgrade (ISSU), NSR is achieved by stateful switchover (SSO) of both TCP and BGP.

NSR does not force any software upgrades on other routers in the network, and peer routers are not required to support NSR.

When a route processor switchover occurs due to a fault, the TCP connections and the BGP sessions are migrated transparently to the standby route processor, and the standby route processor becomes active. The existing protocol state is maintained on the standby route processor when it becomes active, and the protocol state does not need to be refreshed by peers.

Events such as soft reconfiguration and policy modifications can trigger the BGP internal state to change. To ensure state consistency between active and standby BGP processes during such events, the concept of post-it is introduced that act as synchronization points.

BGP NSR provides the following features:

  • NSR-related alarms and notifications

  • Configured and operational NSR states are tracked separately

  • NSR statistics collection

  • NSR statistics display using show commands

  • XML schema support

  • Auditing mechanisms to verify state synchronization between active and standby instances

  • CLI commands to enable and disable NSR

BGP Route Reflectors Reference

#concept_305B2C3244D5404F9E6207098D05CA9E__ illustrates a simple iBGP configuration with three iBGP speakers (routers A, B, and C). Without route reflectors, when Router A receives a route from an external neighbor, it must advertise it to both routers B and C. Routers B and C do not readvertise the iBGP learned route to other iBGP speakers because the routers do not pass on routes learned from internal neighbors to other internal neighbors, thus preventing a routing information loop.

With route reflectors, all iBGP speakers need not be fully meshed because there is a method to pass learned routes to neighbors. In this model, an iBGP peer is configured to be a route reflector responsible for passing iBGP learned routes to a set of iBGP neighbors. In #concept_305B2C3244D5404F9E6207098D05CA9E__ , Router B is configured as a route reflector. When the route reflector receives routes advertised from Router A, it advertises them to Router C, and vice versa. This scheme eliminates the need for the iBGP session between routers A and C.

The internal peers of the route reflector are divided into two groups: client peers and all other routers in the autonomous system (nonclient peers). A route reflector reflects routes between these two groups. The route reflector and its client peers form a cluster. The nonclient peers must be fully meshed with each other, but the client peers need not be fully meshed. The clients in the cluster do not communicate with iBGP speakers outside their cluster.

#concept_305B2C3244D5404F9E6207098D05CA9E__ illustrates a more complex route reflector scheme. Router A is the route reflector in a cluster with routers B, C, and D. Routers E, F, and G are fully meshed, nonclient routers.

When the route reflector receives an advertised route, depending on the neighbor, it takes the following actions:

  • A route from an external BGP speaker is advertised to all clients and nonclient peers.

  • A route from a nonclient peer is advertised to all clients.

  • A route from a client is advertised to all clients and nonclient peers. Hence, the clients need not be fully meshed.

Along with route reflector-aware BGP speakers, it is possible to have BGP speakers that do not understand the concept of route reflectors. They can be members of either client or nonclient groups, allowing an easy and gradual migration from the old BGP model to the route reflector model. Initially, you could create a single cluster with a route reflector and a few clients. All other iBGP speakers could be nonclient peers to the route reflector and then more clusters could be created gradually.

An autonomous system can have multiple route reflectors. A route reflector treats other route reflectors just like other iBGP speakers. A route reflector can be configured to have other route reflectors in a client group or nonclient group. In a simple configuration, the backbone could be divided into many clusters. Each route reflector would be configured with other route reflectors as nonclient peers (thus, all route reflectors are fully meshed). The clients are configured to maintain iBGP sessions with only the route reflector in their cluster.

Usually, a cluster of clients has a single route reflector. In that case, the cluster is identified by the router ID of the route reflector. To increase redundancy and avoid a single point of failure, a cluster might have more than one route reflector. In this case, all route reflectors in the cluster must be configured with the cluster ID so that a route reflector can recognize updates from route reflectors in the same cluster. All route reflectors serving a cluster should be fully meshed and all of them should have identical sets of client and nonclient peers.

By default, the clients of a route reflector are not required to be fully meshed and the routes from a client are reflected to other clients. However, if the clients are fully meshed, the route reflector need not reflect routes to clients.

As the iBGP learned routes are reflected, routing information may loop. The route reflector model has the following mechanisms to avoid routing loops:

  • Originator ID is an optional, nontransitive BGP attribute. It is a 4-byte attributed created by a route reflector. The attribute carries the router ID of the originator of the route in the local autonomous system. Therefore, if a misconfiguration causes routing information to come back to the originator, the information is ignored.

  • Cluster-list is an optional, nontransitive BGP attribute. It is a sequence of cluster IDs that the route has passed. When a route reflector reflects a route from its clients to nonclient peers, and vice versa, it appends the local cluster ID to the cluster-list. If the cluster-list is empty, a new cluster-list is created. Using this attribute, a route reflector can identify if routing information is looped back to the same cluster due to misconfiguration. If the local cluster ID is found in the cluster-list, the advertisement is ignored.

iBGP Multipath Load Sharing Reference

When there are multiple border BGP routers having reachability information heard over eBGP, if no local policy is applied, the border routers will choose their eBGP paths as best. They advertise that bestpath inside the ISP network. For a core router, there can be multiple paths to the same destination, but it will select only one path as best and use that path for forwarding. iBGP multipath load sharing adds the ability to enable load sharing among multiple equi-distant paths. Configuring multiple iBGP best paths enables a router to evenly share the traffic destined for a particular site. The iBGP Multipath Load Sharing feature functions similarly in a Multiprotocol Label Switching (MPLS) Virtual Private Network (VPN) with a service provider backbone.

For multiple paths to the same destination to be considered as multipaths, the following criteria must be met:

  • All attributes must be the same. The attributes include weight, local preference, autonomous system path (entire attribute and not just length), origin code, Multi Exit Discriminator (MED), and Interior Gateway Protocol (iGP) distance.

  • The next hop router for each multipath must be different.

Even if the criteria are met and multiple paths are considered multipaths, the BGP speaking router designates one of the multipaths as the best path and advertises this best path to its neighbors.

Note


  • Overwriting of next-hop calculation for multipath prefixes is not allowed. The next-hop-unchanged multipath command disables overwriting of next-hop calculation for multipath prefixes.

  • The ability to ignore as-path onwards while computing multipath is added. The bgp multipath as-path ignore onwards command ignores as-path onwards while computing multipath.


L3VPN iBGP PE-CE Reference

When BGP is used as the provider edge (PE) or the customer edge (CE) routing protocol, the peering sessions are configured as external peering between the VPN provider autonomous system (AS) and the customer network autonomous system. The L3VPN iBGP PE-CE feature enables the PE and CE devices to exchange Border Gateway Protocol (BGP) routing information by peering as internal Border Gateway Protocol (iBGP) instead of the widely-used external BGP peering between the PE and the CE. This mechanism applies at each PE device where a VRF-based CE is configured as iBGP. This eliminates the need for service providers (SPs) to configure autonomous system override for the CE. With this feature enabled, there is no need to configure the virtual private network (VPN) sites using different autonomous systems.

The neighbor internal-vpn-client command enables PE devices to make an entire VPN cloud act as an internal VPN client to the CE devices. These CE devices are connected internally to the VPN cloud through the iBGP PE-CE connection inside the VRF. After this connection is established, the PE device encapsulates the CE-learned path into an attribute called ATTR_SET and carries it in the iBGP-sourced path throughout the VPN core to the remote PE device. At the remote PE device, this attribute is assigned with individual attributes and the source CE path is extracted and sent to the remote CE devices.

ATTR_SET is an optional transitive attribute that carries the CE path attributes received. The ATTR_SET attribute is encoded inside the BGP update message as follows:

										+------------------------------+
          | Attr Flags (O|T) Code = 128  |
          +------------------------------+
          | Attr. Length (1 or 2 octets) |
          +------------------------------+
          | Origin AS (4 octets)         |
          +------------------------------+
          | Path attributes (variable)   |
          +------------------------------+

Origin AS is the AS of the VPN customer for which the ATTR_SET is generated. The minimum length of ATTR_SET is four bytes and the maximum is the maximum supported for a path attribute after taking into consideration the mandatory fields and attributes in the BGP update message. It is recommended that the maximum length is limited to 3500 bytes. ATTR_SET must not contain the following attributes: MP_REACH, MP_UNREACH, NEW_AS_PATH, NEW_AGGR, NEXT_HOP and ATTR_SET itself (ATTR_SET inside ATTR_SET). If these attributes are found inside the ATTR_SET, the ATTR_SET is considered invalid and the corresponding error handling mechanism is invoked.

MPLS VPN Carrier Supporting Carrier

Carrier supporting carrier (CSC) is a term used to describe a situation in which one service provider allows another service provider to use a segment of its backbone network. The service provider that provides the segment of the backbone network to the other provider is called the backbone carrier. The service provider that uses the segment of the backbone network is called the customer carrier.

A backbone carrier offers Border Gateway Protocol and Multiprotocol Label Switching (BGP/MPLS) VPN services. The customer carrier can be either:

  • An Internet service provider (ISP) (By definition, an ISP does not provide VPN service.)

  • A BGP/MPLS VPN service provider

You can configure a CSC network to enable BGP to transport routes and MPLS labels between the backbone carrier provider edge (PE) routers and the customer carrier customer edge (CE) routers using multiple paths. The benefits of using BGP to distribute IPv4 routes and MPLS label routes are:

  • BGP takes the place of an Interior Gateway Protocol (IGP) and Label Distribution Protocol (LDP) in a VPN routing and forwarding (VRF) table. You can use BGP to distribute routes and MPLS labels. Using a single protocol instead of two simplifies the configuration and troubleshooting.

  • BGP is the preferred routing protocol for connecting two ISPs, mainly because of its routing policies and ability to scale. ISPs commonly use BGP between two providers. This feature enables those ISPs to use BGP.

For detailed information on configuring MPLS VPN CSC with BGP, see the Implementing MPLS Layer 3 VPNs on module of the MPLS Configuration Guide.

Per VRF and Per CE Label for IPv6 Provider Edge

The per VRF and per CE label for IPv6 feature makes it possible to save label space by allocating labels per default VRF or per CE nexthop.

All IPv6 Provider Edge (6PE) labels are allocated per prefix by default. Each prefix that belongs to a VRF instance is advertised with a single label, causing an additional lookup to be performed in the VRF forwarding table to determine the customer edge (CE) next hop for the packet.

However, use the label-allocation-mode command with the per-ce keyword or the per-vrf keyword to avoid the additional lookup on the PE router and conserve label space.

Use per-ce keyword to specify that the same label be used for all the routes advertised from a unique customer edge (CE) peer router. Use the per-vrf keyword to specify that the same label be used for all the routes advertised from a unique VRF.

IPv6 Unicast Routing

Cisco provides complete Internet Protocol Version 6 (IPv6) unicast capability.

An IPv6 unicast address is an identifier for a single interface, on a single node. A packet that is sent to a unicast address is delivered to the interface identified by that address. Cisco IOS XR software supports the following IPv6 unicast address types:

  • Global aggregatable address

  • Site-local address

  • Link-local address

  • IPv4-compatible IPv6 address

For more information on IPv6 unicast addressing, refer the IP Addresses and Services Configuration Guide.

Remove and Replace Private AS Numbers from AS Path in BGP

Private autonomous system numbers (ASNs) are used by Internet Service Providers (ISPs) and customer networks to conserve globally unique AS numbers. Private AS numbers cannot be used to access the global Internet because they are not unique. AS numbers appear in eBGP AS paths in routing updates. Removing private ASNs from the AS path is necessary if you have been using private ASNs and you want to access the global Internet.

Public AS numbers are assigned by InterNIC and are globally unique. They range from 1 to 64511. Private AS numbers are used to conserve globally unique AS numbers, and they range from 64512 to 65535. Private AS numbers cannot be leaked to a global BGP routing table because they are not unique, and BGP best path calculations require unique AS numbers. Therefore, it might be necessary to remove private AS numbers from an AS path before the routes are propagated to a BGP peer.

External BGP (eBGP) requires that globally unique AS numbers be used when routing to the global Internet. Using private AS numbers (which are not unique) would prevent access to the global Internet. The remove and replace private AS Numbers from AS Path in BGP feature allows routers that belong to a private AS to access the global Internet. A network administrator configures the routers to remove private AS numbers from the AS path contained in outgoing update messages and optionally, to replace those numbers with the ASN of the local router, so that the AS Path length remains unchanged.

The ability to remove and replace private AS numbers from the AS Path is implemented in the following ways:

  • The remove-private-as command removes private AS numbers from the AS path even if the path contains both public and private ASNs.

  • The remove-private-as command removes private AS numbers even if the AS path contains only private AS numbers. There is no likelihood of a 0-length AS path because this command can be applied to eBGP peers only, in which case the AS number of the local router is appended to the AS path.

  • The remove-private-as command removes private AS numbers even if the private ASNs appear before the confederation segments in the AS path.

  • The replace-as command replaces the private AS numbers being removed from the path with the local AS number, thereby retaining the same AS path length.

The feature can be applied to neighbors per address family (address family configuration mode). Therefore, you can apply the feature for a neighbor in one address family and not on another, affecting update messages on the outbound side for only the address family for which the feature is configured.

Use show bgp neighbors and show bgp update-group commands to verify that the that private AS numbers were removed or replaced.

BGP Update Message Error Handling

The BGP UPDATE message error handling changes BGP behavior in handling error UPDATE messages to avoid session reset. Based on the approach described in IETF IDR I-D:draft-ietf-idr-error-handling, the Cisco IOS XR BGP UPDATE Message Error handling implementation classifies BGP update errors into various categories based on factors such as, severity, likelihood of occurrence of UPDATE errors, or type of attributes. Errors encountered in each category are handled according to the draft. Session reset will be avoided as much as possible during the error handling process. Error handling for some of the categories are controlled by configuration commands to enable or disable the default behavior.

According to the base BGP specification, a BGP speaker that receives an UPDATE message containing a malformed attribute is required to reset the session over which the offending attribute was received. This behavior is undesirable as a session reset would impact not only routes with the offending attribute, but also other valid routes exchanged over the session.

BGP Error Handling and Attribute Filtering Syslog Messages

When a router receives a malformed update packet, an ios_msg of type ROUTING-BGP-3-MALFORM_UPDATE is printed on the console. This is rate limited to 1 message per minute across all neighbors. For malformed packets that result in actions "Discard Attribute" (A5) or "Local Repair" (A6), the ios_msg is printed only once per neighbor per action. This is irrespective of the number of malformed updates received since the neighbor last reached an "Established" state.

This is a sample BGP error handling syslog message:

%ROUTING-BGP-3-MALFORM_UPDATE : Malformed UPDATE message received from neighbor 13.0.3.50 - message length 90 bytes,
 error flags 0x00000840, action taken "TreatAsWithdraw". 
Error details: "Error 0x00000800, Field "Attr-missing", Attribute 1 (Flags 0x00, Length 0), Data []"

This is a sample BGP attribute filtering syslog message for the "discard attribute" action:

[4843.46]RP/0/RP0/CPU0:Aug 21 17:06:17.919 : bgp[1037]: %ROUTING-BGP-5-UPDATE_FILTERED : 
One or more attributes were filtered from UPDATE message received from neighbor 40.0.101.1 - message length 173 bytes,
 action taken "DiscardAttr".
 Filtering details: "Attribute 16 (Flags 0xc0): Action "DiscardAttr"". NLRIs: [IPv4 Unicast] 88.2.0.0/17

This is a sample BGP attribute filtering syslog message for the "treat-as-withdraw" action:

[391.01]RP/0/RP0/CPU0:Aug 20 19:41:29.243 : bgp[1037]: %ROUTING-BGP-5-UPDATE_FILTERED :
 One or more attributes were filtered from UPDATE message received from neighbor 40.0.101.1 - message length 166 bytes,
 action taken "TreatAsWdr".
 Filtering details: "Attribute 4 (Flags 0xc0): Action "TreatAsWdr"". NLRIs: [IPv4 Unicast] 88.2.0.0/17

BGP-RIB Feedback Mechanism for Update Generation

The Border Gateway Protocol-Routing Information Base (BGP-RIB) feedback mechanism for update generation feature avoids premature route advertisements and subsequent packet loss in a network. This mechanism ensures that routes are installed locally, before they are advertised to a neighbor.

BGP waits for feedback from RIB indicating that the routes that BGP installed in RIB are installed in forwarding information base (FIB) before BGP sends out updates to the neighbors. RIB uses the the BCDL feedback mechanism to determine which version of the routes have been consumed by FIB, and updates the BGP with that version. BGP will send out updates of only those routes that have versions up to the version that FIB has installed. This selective update ensures that BGP does not send out premature updates resulting in attracting traffic even before the data plane is programmed after router reload, LC OIR, or flap of a link where an alternate path is made available.

To configure BGP to wait for feedback from RIB indicating that the routes that BGP installed in RIB are installed in FIB, before BGP sends out updates to neighbors, use the update wait-install command in router address-family IPv4 or router address-family VPNv4 configuration mode. The show bgp , show bgp neighbors , and show bgp process performance-statistics commands display the information from update wait-install configuration.

Use-defined Martian Check

The solution allows disabling the Martian check for these IP address prefixes:

  • IPv4 address prefixes

    • 0.0.0.0/8

    • 127.0.0.0/8

    • 224.0.0.0/4

  • IPv6 address prefixes

    • ::

    • ::0002 - ::ffff

    • ::ffff:a.b.c.d

    • fe80:xxxx

    • ffxx:xxxx

Reduce Recursions for eBGP Peering on Loopback Address on Bridge-Group Virtual Interface

Overview

In a scenario where a native eBGP session establishes an eBGP session between two BGP peers and a customer edge router. The eBGP peer learns the loopback IP address of the BGP neighbor through a static route, which is configured on the Bridge-Group Virtual Interface (BVI) of the customer edge router. Configuring the static route specifying the next hop IP address as the loopback address, nexthop destination address, and the name of the BVI interface results in three levels of recursion. This feature enables you to successfully achieve eBGP peering on a loopback address using a BVI interface. This is done by configuring the static route and specifying the next hop IP address as the loopback address and nexthop destination address without specifying the name of the BVI interface, thus confining to two levels of recursion.

Configure the Reduction of Recursions for eBGP Peering on Loopback Address on Bridge-Group Virtual Interface

Configure the eBGP peering on a loopback address on BVI interface for the reduction of recursions by following these steps:

  • Configure a static route.

  • Configure a VRF.

  • Configure an address family.

  • Configure the static route on a loopback interface.

  • Configure the router to route packets from a network loopback IP address to a next hop destination IP address without specifying the BVI interface name.

The following example shows how to configure a static route specifying the nexthop IP address as the loopback address and the nexthop destination address without specifying the name of the BVI interface.

Router(config)# router static 
Router(config-static)# vrf vrf1 
Router(config-static-vrf)# address-family ipv4 unicast 
Router(config-static-vrf-af)# 192.0.2.1/32 198.51.100.1 --> Loopback static route 
  

Running Configuration


router static 
 vrf vrf1 
  address-family ipv4 unicast 
   192.0.2.1/32 198.51.100.1
  

Verification

The following output displays the BVI interface from which the traffic for the specified destination IP address is being forwarded to the hardware.

Router# show cef 209.165.200.254  hardware egress location 0/0/CPU0 
Mon Apr 25 13:01:53.642 UTC
209.165.200.254 /32, version 24, internal 0x5000001 0x40 (ptr 0x8b7153d8) [1], 0x0 (0x0), 0x0 (0x0)
 Updated Apr 25 13:01:06.124
 Prefix Len 32, traffic index 0, precedence n/a, priority 4
   via 201.201.201.3/32, 2 dependencies, recursive [flags 0x6000] 
    path-idx 0 NHID 0x0 [0x8b714a48 0x8b3890f8]
    next hop 201.201.201.3/32 via 201.201.201.3/32

 
 LEAF - HAL pd context : 
 sub-type : IPV4, ecd_marked:0, has_collapsed_ldi:0
 collapse_bwalk_required:0, ecdv2_marked:0, 
HW Walk:
LEAF:
    PI:0x308b7153d8 PD:0x308b715480 rev:384 type: IPV4 (0) TBL: 0xe0000000
    LEAF location: LEM
    FEC key: 0x2d400010660

 REC-SHLDI HAL PD context :
ecd_marked:0, collapse_bwalk_required:0, load_shared_lb:0

    RSHLDI:
        PI:0x308b609c88 PD:0x308b609da0 rev:382 dpa-rev:149838 flag:0x1
        FEC key: 0x2d400010660 fec index: 0x2001ffcb(131019) num paths: 1 
        p-rev:348  
        Path:0 fec index: 0x2001ffcb(131019) DSP fec index: 0x2001ffd9(131033),

 LEAF - HAL pd context : 
 sub-type : IPV4, ecd_marked:0, has_collapsed_ldi:0
 collapse_bwalk_required:0, ecdv2_marked:0, 
HW Walk:
LEAF:
  PI:0x308b7151b8 PD:0x308b715260 rev:349 type: IPV4 (0) TBL: 0xe0000000
  LEAF location: LEM
  FEC key: 0x26400010660

  LWLDI:
    BVI LDI:
    PI:0x308b6e16b8 PD:0x308b6e1700 rev:348 dpa-rev:141896 p-rev:347 
    FEC key: 0x26400010660 fec index: 0x2001ffcc(131020) num paths:1 
    Path:0  fec index: 0x2001ffcc(131020) BPORT-IFH: 0xf8 DSP:0x0

  SHLDI: (SHARED)
    PI:0x308b60d3a8 PD:0x308b60d4c0 rev:344 dpa-rev:141893 cbf_enabled:0 pbts_enabled:0 flag:0x0
    FEC key: 0x2540001065 fec index: 0x2001ffcd(131021) num paths: 1 bkup paths: 0
    p-rev:343 
    Path:0 fec index: 0x2001ffcd(131021) DSP:0x160030b2 Dest fec index: 0x0(0)

   TX-NHINFO: BVI INTERNAL(UNUSED)
     PI: 0x308d2734a0 PD: 0x308d273528 rev:343 dpa-rev:0
     Trap Port: 0x160030b2 npu_mask: 1
     BVI: Bport ifh: 0 l2frr_enabled: 0 fec: 0 port: 0 encap: 0

   TX-NHINFO:
     PI: 0x308d2732a8 PD: 0x308d273330 rev:347 dpa-rev:141891 Encap hdl: (nil)
     Encap id: 0x40013814 Remote: 0 L3 int: 13 flags: 0x3
     npu_mask: 0x1 DMAC: 10:00:11:11:11:22
     BVI: Bport ifh: 0xf8 l2frr_enabled: 0 fec: 0x2001ffd9 port: 0x1f encap: 0x13811 /* This is 
     the interface from which the traffic for the specified destination IP address 
     is being forwarded to the hardware. */