Cisco Nexus 3548 Switch NX-OS Unicast Routing Configuration Guide, Release 10.2(x)

Information About Advanced BGP

BGP is an interdomain routing protocol that provides loop-free routing between organizations or autonomous systems. Cisco NX-OS supports BGP version 4. BGP version 4 includes multiprotocol extensions that allow BGP to carry routing information for IP routes and multiple Layer 3 protocol address families. BGP uses TCP as a reliable transport protocol to create TCP sessions with other BGP-enabled switches called BGP peers. When connecting to an external organization, the router creates external BGP (eBGP) peering sessions. BGP peers within the same organization exchange routing information through internal BGP (iBGP) peering sessions.

Peer Templates

BGP peer templates allow you to create blocks of common configurations that you can reuse across similar BGP peers. Each block allows you to define a set of attributes that a peer then inherits. You can choose to override some of the inherited attributes as well, making it a very flexible scheme for simplifying the repetitive nature of BGP configurations.

Cisco NX-OS implements three types of peer templates:

The peer-session template defines BGP peer session attributes, such as the transport details, remote autonomous system number of the peer, and session timers. A peer-session template can also inherit attributes from another peer-session template (with locally defined attributes that override the attributes from an inherited peer-session).
A peer-policy template defines the address-family dependent policy aspects for a peer including the inbound and outbound policy, filter-lists, and prefix-lists. A peer-policy template can inherit from a set of peer-policy templates. Cisco NX-OS evaluates these peer-policy templates in the order specified by the preference value in the inherit configuration. The lowest number is preferred over higher numbers.
The peer template can inherit the peer-session and peer-policy templates to allow for simplified peer definitions. It is not mandatory to use a peer template but it can simplify the BGP configuration by providing reusable blocks of configuration.

Authentication

You can configure authentication for a BGP neighbor session. This authentication method adds an MD5 authentication digest to each TCP segment sent to the neighbor to protect BGP against unauthorized messages and TCP security attacks.

Note

The MD5 password must be identical between BGP peers.

Route Policies and Resetting BGP Sessions

You can associate a route policy to a BGP peer. Route policies use route maps to control or modify the routes that BGP recognizes. You can configure a route policy for inbound or outbound route updates. The route policies can match on different criteria, such as a prefix or AS_path attribute, and selectively accept or deny the routes. Route policies can also modify the path attributes.

When you change a route policy applied to a BGP peer, you must reset the BGP sessions for that peer. Cisco NX-OS supports the following three mechanisms to reset BGP peering sessions:

Hard reset—A hard reset tears down the specified peering sessions, including the TCP connection, and deletes routes coming from the specified peer. This option interrupts packet flow through the BGP network. Hard reset is disabled by default.
Soft reconfiguration inbound—A soft reconfiguration inbound triggers routing updates for the specified peer without resetting the session. You can use this option if you change an inbound route policy. Soft reconfiguration inbound saves a copy of all routes received from the peer before processing the routes through the inbound route policy. If you change the inbound route policy, Cisco NX-OS passes these stored routes through the modified inbound route policy to update the route table without tearing down existing peering sessions. Soft reconfiguration inbound can use significant memory resources to store the unfiltered BGP routes. Soft reconfiguration inbound is disabled by default.
Route Refresh—A route refresh updates the inbound routing tables dynamically by sending route refresh requests to supporting peers when you change an inbound route policy. The remote BGP peer responds with a new copy of its routes that the local BGP speaker processes with the modified route policy. Cisco NX-OS automatically sends an outbound route refresh of prefixes to the peer.
BGP peers advertise the route refresh capability as part of the BGP capability negotiation when establishing the BGP peer session. Route refresh is the preferred option and enabled by default.

Note

BGP also uses route maps for route redistribution, route aggregation, route dampening, and other features.

eBGP

External BGP (eBGP) allows you to connect BGP peers from different autonomous systems to exchange routing updates. Connecting to external networks enables traffic from your network to be forwarded to other networks and across the Internet.

You should use loopback interfaces for establishing eBGP peering sessions because loopback interfaces are less susceptible to interface flapping. An interface flap occurs when the interface is administratively brought up or down because of a failure or maintenance issue. See the Configuring eBGP section for information on multihop, fast external failovers, and limiting the size of the AS-path attribute

iBGP

nternal BGP (iBGP) allows you to connect BGP peers within the same autonomous system. You can use iBGP for multihomed BGP networks (networks that have more than one connection to the same external autonomous system).

The following figure shows an iBGP network within a larger BGP network.

iBGP networks are fully meshed. Each iBGP peer has a direct connection to all other iBGP peers to prevent network loops.

Note

You should configure a separate interior gateway protocol in the iBGP network.

AS Confederations

A fully meshed iBGP network becomes complex as the number of iBGP peers grows. You can reduce the iBGP mesh by dividing the autonomous system into multiple subautonomous systems and grouping them into a single confederation. A confederation is a group of iBGP peers that use the same autonomous system number to communicate to external networks. Each subautonomous system is fully meshed within itself and has a few connections to other subautonomous systems in the same confederation.

The following figure shows the BGP network from Figure below, split into two subautonomous systems and one confederation.

In this example, AS10 is split into two subautonomous systems, AS1 and AS2. Each subautonomous system is fully meshed, but there is only one link between the subautonomous systems. By using AS confederations, you can reduce the number of links compared to the fully meshed autonomous system in Figure 1.

Route Reflector

You can alternately reduce the iBGP mesh by using a route reflector configuration. Route reflectors pass learned routes to neighbors so that all iBGP peers do not need to be fully meshed.

Figure 1 shows a simple iBGP configuration with four meshed iBGP speakers (router A, B, C, and D). Without route reflectors, when router A receives a route from an external neighbor, it advertises the route to all three iBGP neighbors.

When you configure an iBGP peer to be a route reflector, it becomes responsible for passing iBGP learned routes to a set of iBGP neighbors.

In the following figure, router B is the route reflector. When the route reflector receives routes advertised from router A, it advertises (reflects) the routes to routers C and D. Router A no longer has to advertise to both routers C and D.

The route reflector and its client peers form a cluster. You do not have to configure all iBGP peers to act as client peers of the route reflector. You must configure any nonclient peer as fully meshed to guarantee that complete BGP updates reach all peers.

Capabilities Negotiation

A BGP speaker can learn about BGP extensions supported by a peer by using the capabilities negotiation feature. Capabilities negotiation allows BGP to use only the set of features supported by both BGP peers on a link.

If a BGP peer does not support capabilities negotiation, Cisco NX-OS will attempt a new session to the peer without capabilities negotiation if you have configured the address family as IPv4.

Route Dampening

Route dampening is a BGP feature that minimizes the propagation of flapping routes across an internetwork. A route flaps when it alternates between the available and unavailable states in rapid succession.

For example, consider a network with three BGP autonomous systems: AS1, AS2, and AS3. Suppose that a route in AS1 flaps (it becomes unavailable). Without route dampening, AS1 sends a withdraw message to AS2. AS2 propagates the withdrawal message to AS3. When the flapping route reappears, AS1 sends an advertisement message to AS2, which sends the advertisement to AS3. If the route repeatedly becomes unavailable, and then available, AS1 sends many withdrawal and advertisement messages that propagate through the other autonomous systems.

Route dampening can minimize flapping. Suppose that the route flaps. AS2 (in which route dampening is enabled) assigns the route a penalty of 1000. AS2 continues to advertise the status of the route to neighbors. Each time that the route flaps, AS2 adds to the penalty value. When the route flaps so often that the penalty exceeds a configurable suppression limit, AS2 stops advertising the route, regardless of how many times that it flaps. The route is now dampened.

The penalty placed on the route decays until the reuse limit is reached. At that time, AS2 advertises the route again. When the reuse limit is at 50 percent, AS2 removes the dampening information for the route.

Note

The router does not apply a penalty to a resetting BGP peer when route dampening is enabled, even though the peer reset withdraws the route.

Load Sharing and Multipath

BGP can install multiple equal-cost eBGP or iBGP paths into the routing table to reach the same destination prefix. Traffic to the destination prefix is then shared across all the installed paths.

The BGP best-path algorithm considers the paths as equal-cost paths if the following attributes are identical:

Weight
Local preference
AS_path
Origin code
Multi-exit discriminator (MED)
IGP cost to the BGP next hop

BGP selects only one of these multiple paths as the best path and advertises the path to the BGP peers.

Note

Paths received from different AS confederations are considered as equal-cost paths if the external AS_path values and the other attributes are identical.

Note

When you configure a route reflector for iBGP multipath, and the route reflector advertises the selected best path to its peers, the next hop for the path is not modified.

Route Aggregation

You can configure aggregate addresses. Route aggregation simplifies route tables by replacing a number of more specific addresses with an address that represents all the specific addresses. For example, you can replace these three more specific addresses, 10.1.1.0/24, 10.1.2.0/24, and 10.1.3.0/24 with one aggregate address, 10.1.0.0/16.

Aggregate prefixes are present in the BGP route table so that fewer routes are advertised.

Note

Cisco NX-OS does not support automatic route aggregation.

Route aggregation can lead to forwarding loops. To avoid this problem, when BGP generates an advertisement for an aggregate address, it automatically installs a summary discard route for that aggregate address in the local routing table. BGP sets the administrative distance of the summary discard to 220 and sets the route type to discard. BGP does not use discard routes for next-hop resolution.

BGP Conditional Advertisement

BGP conditional advertisement allows you to configure BGP to advertise or withdraw a route based on whether or not a prefix exists in the BGP table. This feature is useful, for example, in multihomed networks, in which you want BGP to advertise some prefixes to one of the providers only if information from the other provider is not present.

Consider an example network with three BGP autonomous systems: AS1, AS2, and AS3, where AS1 and AS3 connect to the Internet and to AS2. Without conditional advertisement, AS2 propagates all routes to both AS1 and AS3. With conditional advertisement, you can configure AS2 to advertise certain routes to AS3 only if routes from AS1 do not exist (if for example, the link to AS1 fails).

BGP conditional advertisement adds an exist or not-exist test to each route that matches the configured route map. See the Configuring BGP Conditional Advertisement section for more information.

BGP Next-Hop Address Tracking

BGP monitors the next-hop address of installed routes to verify next-hop reachability and to select, install, and validate the BGP best path. BGP next-hop address tracking speeds up this next-hop reachability test by triggering the verification process when routes change in the RIB that may affect BGP next-hop reachability.

BGP receives notifications from the RIB when next-hop information changes (event-driven notifications). 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 changes.
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.

Event notifications from the RIB are classified as critical and noncritical. Notifications for critical and noncritical events are sent in separate batches. However, a noncritical event is sent 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.

See the Configuring BGP Next-Hop Address Tracking section for more information.

Route Redistribution

You can configure BGP to redistribute static routes or routes from other protocols. You configure a route policy with the redistribution to control which routes are passed into BGP. A route policy allows you to filter routes based on attributes such as the destination, origination protocol, route type, route tag, and so on. See Configuring Route Policy Manager, for more information.

Tuning BGP

You can modify the default behavior of BGP through BGP timers and by adjusting the best-path algorithm.

BGP Timers

BGP uses different types of timers for neighbor session and global protocol events. Each established session has a minimum of two timers for sending periodic keepalive messages and for timing out sessions when peer keepalives do not arrive within the expected time. In addition, there are other timers for handling specific features. Typically, you configure these timers in seconds. The timers include a random adjustment so that the same timers on different BGP peers trigger at different times.

Tuning the Best-Path Algorithm

You can modify the default behavior of the best-path algorithm through optional configuration parameters, including changing how the algorithm handles the MED attribute and the router ID.

Multiprotocol BGP

BGP on Cisco NX-OS supports multiple address families. Multiprotocol BGP (MP-BGP) carries different sets of routes depending on the address family. For example, BGP can carry one set of routes for IPv4 unicast routing. You can use MP-BGP for reverse-path forwarding (RPF) checks in IP multicast networks.

Note

Because Multicast BGP does not propagate multicast state information, you need a multicast protocol, such as Protocol Independent Multicast (PIM).

Use the router address-family and neighbor address-family configuration modes to support multiprotocol BGP configurations. MP-BGP maintains separate RIBs for each configured address family, such as a unicast RIB and a multicast RIB for BGP.

A multiprotocol BGP network is backward compatible but BGP peers that do not support multiprotocol extensions cannot forward routing information, such as address family identifier information, that the multiprotocol extensions carry.

Prerequisites for BGP

BGP has the following prerequisites:

You must enable the BGP feature (see the Enabling the BGP Feature section).
You should have a valid router ID configured on the system.
You must have an AS number, either assigned by a Regional Internet Registry (RIR) or locally administered.
You must have reachability (such as an interior gateway protocol (IGP), a static route, or a direct connection) to the peer that you are trying to make a neighbor relationship with.
You must explicitly configure an address family under a neighbor for the BGP session establishment.

Guidelines and Limitations for Advanced BGP

BGP has the following configuration guidelines and limitations:

Prefix peering operates only in passive TCP mode. It accepts incoming connections from remote peers if the peer address falls within the prefix.
The dynamic autonomous system number prefix peer configuration overrides the individual autonomous system number configuration that is inherited from a BGP template.
If you configure a dynamic autonomous system number for prefix peers in an autonomous system confederation, BGP establishes sessions with only the autonomous system numbers in the local confederation.
BGP sessions that are created through a dynamic autonomous system number prefix peer ignore any configured eBGP multihop time-to-live (TTL) value or a disabled check for directly connected peers.
Configure a router ID for BGP to avoid automatic router ID changes and session flaps.
Use the maximum-prefix configuration option per peer to restrict the number of routes that are received and system resources used.
Configure the update-source to establish a session with eBGP multihop sessions.
Specify a BGP route map if you configure redistribution.
Configure the BGP router ID within a VRF.
If you decrease the keepalive and hold timer values, the network might experience session flaps.

Default Settings for BGP

Table below lists the default settings for BGP parameters.

Table 1. Default BGP Parameters
Parameters	Default
BGP feature	disabled
keep alive interval	60 seconds
hold timer	180 seconds

Configuring Advanced BGP

Note

If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature might differ from the Cisco IOS commands that you would use.

Configuring BGP Session Templates

You can use BGP session templates to simplify BGP configuration for multiple BGP peers with similar configuration needs. BGP templates allow you to reuse common configuration blocks. You configure BGP templates first, and then apply these templates to BGP peers.

With BGP session templates, you can configure session attributes such as inheritance, passwords, timers, and security.

A peer-session template can inherit from one other peer-session template. You can configure the second template to inherit from a third template. The first template also inherits this third template. This indirect inheritance can continue for up to seven peer-session templates.

Any attributes configured for the neighbor take priority over any attributes inherited by that neighbor from a BGP template.

Before you begin

Ensure that you have enabled the BGP feature (see the Enabling the BGP Feature section).

SUMMARY STEPS

configure terminal
router bgp autonomous-system-number
template peer-session template-name
(Optional) password number password
(Optional) timers keepalive hold
exit
neighbor ip-address remote-as as-number
inherit peer-session template-name
(Optional) description text
(Optional) show bgp peer-session template-name
(Optional) copy running-config startup-config

DETAILED STEPS

	Command or Action	Purpose
Step 1	configure terminal Example: `switch# configure terminal switch(config)#`	Enters configuration mode.
Step 2	router bgp `autonomous-system-number` Example: `switch(config)# router bgp 65536 switch(config-router)#`	Enables BGP and assigns the autonomous system number to the local BGP speaker.
Step 3	template peer-session `template-name` Example: `switch(config-router)# template peer-session BaseSession switch(config-router-stmp)#`	Enters peer-session template configuration mode.
Step 4	(Optional) password `number password` Example: `switch(config-router-stmp)# password 0 test`	(Optional) Adds the clear text password test to the neighbor. The password is stored and displayed in type 3 encrypted form (3DES).
Step 5	(Optional) timers `keepalive hold` Example: `switch(config-router-stmp)# timers 30 90`	(Optional) Adds the BGP keepalive and holdtimer values to the peer-session template. The default keepalive interval is 60. The default hold time is 180.
Step 6	exit Example: `switch(config-router-stmp)# exit switch(config-router)#`	Exits peer-session template configuration mode.
Step 7	neighbor `ip-address` remote-as `as-number` Example: `switch(config-router)# neighbor 192.168.1.2 remote-as 65536 switch(config-router-neighbor)#`	Places the router in the neighbor configuration mode for BGP routing and configures the neighbor IP address.
Step 8	inherit peer-session `template-name` Example: `switch(config-router-neighbor)# inherit peer-session BaseSession switch(config-router-neighbor)`	Applies a peer-session template to the peer.
Step 9	(Optional) description `text` Example: `switch(config-router-neighbor)# description Peer Router A switch(config-router-neighbor)`	(Optional) Adds a description for the neighbor.
Step 10	(Optional) show bgp peer-session `template-name` Example: `switch(config-router-neighbor)# show bgp peer-session BaseSession`	(Optional) Displays the peer-policy template.
Step 11	(Optional) copy running-config startup-config Example: `switch(config-router-neighbor)# copy running-config startup-config`	(Optional) Saves this configuration change.

Example

Use the show bgp neighbor command to see the template applied. See the Cisco Nexus 3000 Series Command Reference for details on all commands available in the template.

This example shows how to configure a BGP peer-session template and apply it to a BGP peer:

switch# configure terminal
switch(config)# router bgp 65536
switch(config-router)# template peer-session BaseSession
switch(config-router-stmp)# timers 30 90
switch(config-router-stmp)# exit
switch(config-router)# neighbor 192.168.1.2 remote-as 65536
switch(config-router-neighbor)# inherit peer-session BaseSession
switch(config-router-neighbor)# description Peer Router A
switch(config-router-neighbor)# address-family ipv4 unicast
switch(config-router-neighbor)# copy running-config startup-config

Configuring BGP Peer-Policy Templates

You can configure a peer-policy template to define attributes for a particular address family. You assign a preference to each peer-policy template and these templates are inherited in the order specified, for up to five peer-policy templates in a neighbor address family.

Cisco NX-OS evaluates multiple peer policies for an address family using the preference value. The lowest preference value is evaluated first. Any attributes configured for the neighbor take priority over any attributes inherited by that neighbor from a BGP template.

Peer-policy templates can configure address family-specific attributes such as AS-path filter lists, prefix lists, route reflection, and soft reconfiguration.

Before you begin

Ensure that you have enabled the BGP feature (see the Enabling the BGP Feature section).

SUMMARY STEPS

configure terminal
router bgp autonomous-system-number
template peer-policy template-name
(Optional) advertise-active-only
(Optional) maximum-prefix number
exit
neighbor ip-address remote-as as-number
address-family ipv4 unicast
inherit peer-policy template-name preference
(Optional) show bgp peer-policy template-name
(Optional) copy running-config startup-config

DETAILED STEPS

	Command or Action	Purpose
Step 1	configure terminal Example: `switch# configure terminal switch(config)#`	Enters configuration mode.
Step 2	router bgp `autonomous-system-number` Example: `switch(config)# router bgp 65536 switch(config-router)#`	Enables BGP and assigns the autonomous system number to the local BGP speaker.
Step 3	template peer-policy `template-name` Example: `switch(config-router)# template peer-policy BasePolicy switch(config-router-ptmp)#`	Creates a peer-policy template.
Step 4	(Optional) advertise-active-only Example: `switch(config-router-ptmp)# advertise-active-only`	(Optional) Advertises only active routes to the peer.
Step 5	(Optional) maximum-prefix `number` Example: `switch(config-router-ptmp)# maximum-prefix 20`	(Optional) Sets the maximum number of prefixes allowed from this peer.
Step 6	exit Example: `switch(config-router-ptmp)# exit switch(config-router)#`	Exits peer-policy template configuration mode.
Step 7	neighbor `ip-address` remote-as `as-number` Example: `switch(config-router)# neighbor 192.168.1.2 remote-as 65536 switch(config-router-neighbor)#`	Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address.
Step 8	address-family ipv4 unicast Example: `switch(config-router-neighbor)# address-family ipv4 unicast switch(config-router-neighbor-af)#`	Enters global address family configuration mode for the specified address family.
Step 9	inherit peer-policy `template-name preference` Example: `switch(config-router-neighbor-af)# inherit peer-policy BasePolicy 1`	Applies a peer-policy template to the peer address family configuration and assigns the preference value for this peer policy.
Step 10	(Optional) show bgp peer-policy `template-name` Example: `switch(config-router-neighbor-af)# show bgp peer-policy BasePolicy`	(Optional) Displays the peer-policy template.
Step 11	(Optional) copy running-config startup-config Example: `switch(config-router-neighbor)# copy running-config startup-config`	(Optional) Saves this configuration change.

Example

Use the show bgp neighbor command to see the template applied. See the Cisco Nexus 3000 Series Command Reference for details on all commands available in the template.

This example shows how to configure a BGP peer-session template and apply it to a BGP peer:

switch# configure terminal
switch(config)# router bgp 65536
switch(config-router)# template peer-session BasePolicy
switch(config-router-ptmp)# maximum-prefix 20
switch(config-router-ptmp)# exit
switch(config-router)# neighbor 192.168.1.1 remote-as 65536
switch(config-router-neighbor)# address-family ipv4 unicast
switch(config-router-neighbor-af)# inherit peer-policy BasePolicy
switch(config-router-neighbor-af)# copy running-config startup-config

Configuring BGP Peer Templates

You can configure BGP peer templates to combine session and policy attributes in one reusable configuration block. Peer templates can also inherit peer-session or peer-policy templates. Any attributes configured for the neighbor take priority over any attributes inherited by that neighbor from a BGP template. You configure only one peer template for a neighbor, but that peer template can inherit peer-session and peer-policy templates.

Peer templates support session and address family attributes, such as eBGP multihop time-to-live, maximum prefix, next-hop self, and timers.

Before you begin

Ensure that you have enabled the BGP feature (see the Enabling the BGP Feature section).

SUMMARY STEPS

configure terminal
router bgp autonomous-system-number
template peer-session template-name
(Optional) inherit peer-session template-name
address-family ipv4 unicast
(Optional) inherit peer template-name
exit
(Optional) timers keepalive hold
exit
neighbor ip-address remote-as as-number
inherit peer template-name
(Optional) timers keepalive hold
(Optional) show bgp peer-template template-name
(Optional) copy running-config startup-config

DETAILED STEPS

	Command or Action	Purpose
Step 1	configure terminal Example: `switch# configure terminal switch(config)#`	Enters configuration mode.
Step 2	router bgp `autonomous-system-number` Example: `switch(config)# router bgp 65536 switch(config-router)#`	Enables BGP and assigns the autonomous system number to the local BGP speaker.
Step 3	template peer-session `template-name` Example: `switch(config-router)# template peer-session BaseSession switch(config-router-stmp)#`	Enters peer-session template configuration mode.
Step 4	(Optional) inherit peer-session `template-name` Example: `switch(config-router-neighbor)# inherit peer-session BaseSession`	(Optional) Inherits a peer-session template in the peer template.
Step 5	address-family ipv4 unicast Example: `switch(config-router-neighbor)# address-family ipv4 unicast switch(config-router-neighbor-af)#`	Configures the global address family configuration mode for the specified address family.
Step 6	(Optional) inherit peer `template-name` Example: `switch(config-router-neighbor-af)# inherit peer BasePolicy`	(Optional) Applies a peer template to the neighbor address family configuration.
Step 7	exit Example: `switch(config-router-neighbor-af)# exit switch(config-router-neighbor)#`	Exits BGP neighbor address family configuration mode.
Step 8	(Optional) timers `keepalive hold` Example: `switch(config-router-neighbor)# timers 45 100`	(Optional) Adds the BGP timer values to the peer. These values override the timer values in the peer-session template, BaseSession.
Step 9	exit Example: `switch(config-router-stmp)# exit switch(config-router)#`	Exits BGP peer template configuration mode.
Step 10	neighbor `ip-address` remote-as `as-number` Example: `switch(config-router)# neighbor 192.168.1.2 remote-as 65536 switch(config-router-neighbor)#`	Places the router in the neighbor configuration mode for BGP routing and configures the neighbor IP address.
Step 11	inherit peer `template-name` Example: `switch(config-router-neighbor)# inherit peer BasePeer`	Inherits the peer template.
Step 12	(Optional) timers `keepalive hold` Example: `switch(config-router-neighbor)# timers 60 120`	(Optional) Adds the BGP timer values to this neighbor. These values override the timer values in the peer template and the peer-session template.
Step 13	(Optional) show bgp peer-template `template-name` Example: `switch(config-router-neighbor-af)# show bgp peer-template BasePeer`	(Optional) Displays the peer template.
Step 14	(Optional) copy running-config startup-config Example: `switch(config-router-neighbor)# copy running-config startup-config`	(Optional) Saves this configuration change.

Example

Use the show bgp neighbor command to see the template applied. See the Cisco Nexus 3000 Series Command Reference for details on all commands available in the template.

This example shows how to configure a BGP peer template and apply it to a BGP peer:

switch# configure terminal
switch(config)# router bgp 65536
switch(config-router)# template peer BasePeer
switch(config-router-neighbor)# inherit peer-session BaseSession
switch(config-router-neighbor)# address-family ipv4 unicast
switch(config-router-neighbor-af)# inherit peer-policy BasePolicy 1
switch(config-router-neighbor-af)# exit
switch(config-router-neighbor)# exit
switch(config-router)# neighbor 192.168.1.2 remote-as 65536
switch(config-router-neighbor)# inherit peer BasePeer
switch(config-router-neighbor)# copy running-config startup-config

Configuring BGP Interface Peering via IPv6 Link-Local for IPv4 and IPv6 Address Families

You can configure BGP Interface Peering via IPv6 Link-Local for IPv4 and IPv6 Address Families for automatic BGP neighbor discovery using unnumbered interfaces. Doing so allows you to set up BGP sessions using an interface name as a BGP peer (rather than interface-scoped addresses). This feature relies on ICMPv6 neighbor discovery (ND) route advertisement (RA) for automatic neighbor discovery and on RFC 5549 for sending IPv4 routes with IPv6 next hop.

Before you begin

You must enable BGP.

SUMMARY STEPS

configure terminal
router bgp autonomous-system-number
neighbor interface-name remote-as {as-number | route-map map-name}
inherit peer template-name
address-family {ipv4 | ipv6} unicast
(Optional) show bgp {ipv4 | ipv6} unicast neighbors interface
(Optional) show ip bgp neighbors interface-name
(Optional) show ipv6 routers [interface interface]
(Optional) copy running-config startup-config

DETAILED STEPS

Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal

Enters configuration mode.

Step 2

router bgp autonomous-system-number

Example:

switch(config)# router bgp 65535
switch(config-router)#

Enables BGP and assigns the autonomous system number to the local BGP speaker. The AS number can be a 16-bit integer or a 32-bit integer in the form of a higher 16-bit decimal number and a lower 16-bit decimal number in xx.xx format.

Step 3

neighbor interface-name remote-as {as-number | route-map map-name}

Example:

switch(config-router)# neighbor
Ethernet1/1 remote-as route-map Testmap
switch(config-router-neighbor)#

Places the router in the neighbor configuration mode for BGP routing and configures the interface for BGP peering.

Note

You can specify only Ethernet interfaces, port-channel interfaces, subinterfaces, and breakout interfaces.

Beginning with Cisco NX-OS Release 9.3(6), you can specify a route map, which can contain AS lists and ranges. See Dynamic AS Numbers for Prefix Peers for more information about using dynamic AS numbers.

Step 4

inherit peer template-name

Example:

switch(config-router-neighbor)# inherit peer PEER

Inherits the peer template.

Step 5

address-family {ipv4 | ipv6} unicast

Example:

switch(config-router-neighbor)#
address-family ipv4 unicast
switch(config-router-neighbor-af)#

Enters global address family configuration mode for the address family specified.

Step 6

(Optional) show bgp {ipv4 | ipv6} unicast neighbors interface

Example:

switch(config-router-neighbor-af)# show
bgp ipv4 unicast neighbors e1/25

Example:

switch(config-router-neighbor-af)# show
bgp ipv6 unicast neighbors 3FFE:700:20:1::11

(Optional)

Displays information about BGP peers.

Step 7

(Optional) show ip bgp neighbors interface-name

Example:

switch(config-router-neighbor-af)# show ip bgp neighbors Ethernet1/1

(Optional)

Displays the interface used as a BGP peer.

Step 8

(Optional) show ipv6 routers [interface interface]

Example:

switch(config-router-neighbor-af)# show ipv6 routers interface Ethernet1/1

(Optional)

Displays the link-local address of remote IPv6 routers, which is learned through IPv6 ICMP router advertisement.

Step 9

(Optional) copy running-config startup-config

Example:

switch(config-router-neighbor-af)# copy
running-config startup-config

(Optional)

Saves this configuration change.

Example

This example shows how to configure BGP Interface Peering via IPv6 Link-Local for IPv4 and IPv6 Address Families using a route map:

iBGP Interface Peering Configuration for Leaf 1:

switch# configure terminal
switch(config)# route-map Testmap permit 10
switch(config-route-map)# match as-number 100-200, 300, 400
switch(config-route-map)# exit
switch(config)# router bgp 65000
switch(config-router)# neighbor Ethernet1/1 remote-as route-map Testmap
switch(config-router-neighbor)# inherit peer PEER
switch(config-router-neighbor)# address-family ipv4 unicast
switch(config-router-neighbor)# address-family ipv6 unicast
switch(config-router-neighbor-af)# copy running-config startup-config

This example shows sample output for BGP Interface Peering via IPv6 Link-Local for IPv4 and IPv6 Address Families:

switch(config-router-neighbor)# show bgp ipv4 unicast neighbors e1/15.1
BGP neighbor is fe80::2, remote AS 100, ibgp link, Peer index 4
Peer is an instance of interface peering Ethernet1/15.1
BGP version 4, remote router ID 5.5.5.5
Neighbor previous state = OpenConfirm
BGP state = Established, up for 2d16h
Neighbor vrf: default
Peer is directly attached, interface Ethernet1/15.1
Last read 00:00:54, hold time = 180, keepalive interval is 60 seconds
Last written 00:00:08, keepalive timer expiry due 00:00:51
Received 3869 messages, 0 notifications, 0 bytes in queue
Sent 3871 messages, 0 notifications, 0(0) bytes in queue
Enhanced error processing: On
0 discarded attributes
Connections established 2, dropped 1
Last reset by peer 2d16h, due to session closed
Last error length received: 0
Reset error value received 0
Reset error received major: 104 minor: 0
Notification data received:
Last reset by us never, due to No error
Last error length sent: 0
Reset error value sent: 0
Reset error sent major: 0 minor: 0
--More--

Interface Configuration:

IPv6 needs to be enabled on the corresponding interface using one of the following commands:

ipv6 address ipv6-address
ipv6 address use-link-local-only
ipv6 link-local link-local-address

switch# configure terminal
switch(config)# interface Ethernet1/1
switch(config-if)# ipv6 address use-link-local-only

Note

If an IPv4 address is not configured on the interface, the ip forward command must be configured on the interface to enable IPv4 forwarding.

Note

IPv6 ND timers can be tuned to speed up neighbor discovery and for BGP faster route convergence.

switch(config-if)# ipv6 nd ra-interval 4 min 3
switch(config-if)# ipv6 nd ra-lifetime 10

Note

Beginning with Cisco NX-OS Release 9.3(6), for customer deployments with parallel links, the following command must be added in interface mode:

switch(config-if)# ipv6 link-local use-bia

The command makes IPv6 LLA unique across different interfaces.

Configuring BGP Authentication

You can configure BGP to authenticate route updates from peers using MD5 digests.

To configure BGP to use MD5 authentication, use the following command in neighbor configuration mode:


Command	Purpose
password [ 0 \| 3 \| 7 ] `string` Example : `switch(config-router-neighbor)# password BGPpassword`	Configures an MD5 password for BGP neighbor sessions.

Resetting a BGP Session

If you modify a route policy for BGP, you must reset the associated BGP peer sessions. If the BGP peers do not support route refresh, you can configure a soft reconfiguration for inbound policy changes. Cisco NX-OS automatically attempts a soft reset for the session.

To configure soft reconfiguration inbound, use the following command in neighbor address-family configuration mode:


Command	Purpose
soft-reconfiguration inbound Example : `switch(config-router-neighbor-af)# soft-reconfiguration inbound`	Enables soft reconfiguration to store the inbound BGP route updates. This command triggers an automatic soft clear or refresh of BGP neighbor sessions.

To reset a BGP neighbor session, use the following command in any mode:


Command	Purpose
clear bgp ip { unicast } `ip-address` soft { in \| out } Example : `switch# clear bgp ip unicast 192.0.2.1 soft in`	Resets the BGP session without tearing down the TCP session.

Modifying the Next-Hop Address

You can modify the next-hop address used in a route advertisement in the following ways:

Disable the next-hop calculation and use the local BGP speaker address as the next-hop address.
Set the next-hop address as a third-party address. Use this feature in situations where the original next-hop address is on the same subnet as the peer that the route is being sent to. Using this feature saves an extra hop during forwarding.

To modify the next-hop address, use the following parameters in commands address-family configuration mode:


Command	Purpose
next-hop-self Example : `switch(config-router-neighbor-af)# next-hop-self`	Uses the local BGP speaker address as the next-hop address in route updates. This command triggers an automatic soft clear or refresh of BGP neighbor sessions.
next-hop-third-party Example : `switch(config-router-neighbor-af)# next-hop-third-party`	Sets the next-hop address as a third-party address. Use this command for single-hop EBGP peers that do not have next-hop-self configured.

Configuring BGP Next-Hop Address Tracking

BGP next-hop address tracking is enabled by default and cannot be disabled.

You can modify the delay interval between RIB checks to increase the performance of BGP next-hop tracking. You can configure the critical timer for routes that affect BGP next-hop reachability, and you can configure the noncritical timer for all other routes in the BGP table.

To modify the BGP next-hop address tracking, use the following commands address-family configuration mode:


Command	Purpose
nexthop trigger-delay {critical \| non-critical } `milliseconds` Example : `switch(config-router-af)# nexthop trigger-delay critical 5000`	Specifies the next-hop address tracking delay timer for critical next-hop reachability routes and for noncritical routes. The range is from 1 to 4294967295 milliseconds. The critical timer default is 3000. The noncritical timer default is 10000.
nexthop route-map `name` Example : `switch(config-router-af)# nexthop route-map nextHopLimits`	Specifies a route map to match the BGP next-hop addresses to. The name can be any case-sensitive, alphanumeric string up to 63 characters.

Configuring Next-Hop Filtering

BGP next-hop filtering allows you to specify that when a next-hop address is checked with the RIB, the underlying route for that next-hop address is passed through the route map. If the route map rejects the route, the next-hop address is treated as unreachable.

BGP marks all next hops that are rejected by the route policy as invalid and does not calculate the best path for the routes that use the invalid next-hop address.

To configure BGP next-hop filtering, use the following command in address-family configuration mode:


Command	Purpose
nexthop route-map `name` Example : `switch(config-router-af)# nexthop route-map nextHopLimits`	Specifies a route map to match the BGP next-hop route to. The name can be any case-sensitive, alphanumeric string up to 63 characters.

Controlling Reflected Routes Through Next-Hop-Self

NX-OS enables controlling the iBGP routes being sent to a specific peer through the next-hop-self [all] arguments. By using these arguments, you can selectively change the next-hop of routes even if the route is reflected.


Command	Purpose
next-hop-self [all] Example: `switch(config-router-af)# next-hop-self all`	Uses the local BGP speaker address as the next-hop address in route updates. The all keyword is optional. If you specify all , all routes are sent to the peer with next-hop-self. If you do not specify all , the next hops of reflected routes are not changed.

Disabling Capabilities Negotiation

You can disable capabilities negotiations to interoperate with older BGP peers that do not support capabilities negotiation.

To disable capabilities negotiation, use the following command in neighbor configuration mode:


Command	Purpose
dont-capability-negotiate Example : `switch(config-router-neighbor)# dont-capability-negotiate`	Disables capabilities negotiation. You must manually reset the BGP sessions after configuring this command.

Configuring eBGP

This section includes the following topics:

Disabling eBGP Single-Hop Checking

You can configure eBGP to disable checking whether a single-hop eBGP peer is directly connected to the local router. Use this option for configuring a single-hop loopback eBGP session between directly connected switches.

To disable checking whether or not a single-hop eBGP peer is directly connected, use the following command in neighbor configuration mode:


Command	Purpose
disable-connected-check Example : `switch(config-router-neighbor)# disable-connected-check`	Disables checking whether or not a single-hop eBGP peer is directly connected. You must manually reset the BGP sessions after using this command.

Configuring eBGP Multihop

You can configure the eBGP time-to-live (TTL) value to support eBGP multihop. In some situations, an eBGP peer is not directly connected to another eBGP peer and requires multiple hops to reach the remote eBGP peer. You can configure the eBGP TTL value for a neighbor session to allow these multihop sessions.

To configure eBGP multihop, use the following command in neighbor configuration mode:


Command	Purpose
ebgp-multihop `ttl-value` Example : `switch(config-router-neighbor)# ebgp-multihop 5`	Configures the eBGP TTL value for eBGP multihop. The range is from 2 to 255. You must manually reset the BGP sessions after using this command.

Disabling a Fast External Failover

Typically, when a BGP router loses connectivity to a directly connected eBGP peer, BGP triggers a fast external failover by resetting the eBGP session to the peer. You can disable this fast external failover to limit the instability caused by link flaps.

To disable fast external failover, use the following command in router configuration mode:


Command	Purpose
no fast-external-failover Example : `switch(config-router)# no fast-external-failover`	Disables a fast external failover for eBGP peers. This command is enabled by default.

Limiting the AS-path Attribute

You can configure eBGP to discard routes that have a high number of AS numbers in the AS-path attribute.

To discard routes that have a high number of AS numbers in the AS-path attribute, use the following command in router configuration mode:


Command	Purpose
maxas-limit `number` Example : `switch(config-router)# maxas-limit 50`	Discards eBGP routes that have a number of AS-path segments that exceed the specified limit. The range is from 1 to 2000.

Configuring Local AS Support

The local AS feature allows a router to appear to be a member of a second autonomous system (AS), in addition to its real AS. Local AS allows two ISPs to merge without modifying peering arrangements. Routers in the merged ISP become members of the new autonomous system but continue to use their old AS numbers for their customers.

Local AS can only be used for true eBGP peers. You cannot use this feature for two peers that are members of different confederation subautonomous systems.

To configure eBGP local AS support, use the following command in neighbor configuration mode:


Command	Purpose
local-as `number` [ no-prepend [ replace-as [ dual-as ]]] Example : `switch(config-router-neighbor)# local-as 1.1`	Configures eBGP to prepend the local AS `number` to the AS_PATH attribute. The local AS `number` can be a 16-bit integer or a 32-bit integer in the form of a higher 16-bit decimal number and a lower 16-bit decimal number in xx.xx format. The no-prepend keyword ensures that the local AS `number` is not prepended to any downstream BGP neighbors except for the partner who is peering with the local AS `number` . The replace-as keyword ensures that only the local AS `number` of the peering session is prepended to the AS_PATH attribute. The autonomous-system number from the local BGP routing process is not prepended. The dual-as keyword configures the eBGP neighbor to establish a peering session using the real autonomous-system number (from the local BGP routing process) or by using the autonomous-system number configured as the Local AS).

Configuring BGP Attribute Filtering and Error Handling

Beginning with Cisco NX-OS Release 9.3(3), you can configure BGP attribute filtering and error handling to provide an increased level of security. The following features are available and implemented in the following order:

Path attribute treat-as-withdraw: Allows you to treat-as-withdraw a BGP update from a specific neighbor if the update contains a specified attribute type. The prefixes contained in the update are removed from the routing table.
Path attribute discard: Allows you to remove specific path attributes in a BGP update from a specific neighbor.
Enhanced attribute error handling: Prevents peer sessions from flapping due to a malformed update.

Attribute types 1, 2, 3, 4, 5, 8, 14, 15, and 16 cannot be configured for path attribute treat-as-withdraw and path attribute discard. Attribute type 9 (Originator) and type 10 (Cluster-id) can be configured for eBGP neighbors only.

Treating as Withdraw Path Attributes from a BGP Update Message

To "treat-as-withdraw" BGP updates that contain specific path attributes, use the following command in router neighbor configuration mode:

Procedure

Command or Action Purpose

Command or Action	Purpose
[no] path-attribute treat-as-withdraw [`value` \| range `start end`] in Example: `switch#(config-router)# neighbor 10.20.30.40 switch(config-router-neighbor)# path-attribute treat-as-withdraw 100 in` Example: `switch#(config-router)# neighbor 10.20.30.40 switch(config-router-neighbor)# path-attribute treat-as-withdraw range 21 255 in`	Treats as withdraw any incoming BGP update messages that contain the specified path attribute or range of path attributes and triggers an inbound route refresh to ensure that the routing table is up to date. Any prefixes in a BGP update that are treat-as-withdraw are removed from the BGP routing table. This command is also supported for BGP template peers and BGP template peer sessions.

[no] path-attribute treat-as-withdraw [value | range start end] in

Example:

switch#(config-router)# neighbor 10.20.30.40
switch(config-router-neighbor)# path-attribute treat-as-withdraw 100 in

Example:

switch#(config-router)# neighbor 10.20.30.40
switch(config-router-neighbor)# path-attribute treat-as-withdraw range 21 255 in

Treats as withdraw any incoming BGP update messages that contain the specified path attribute or range of path attributes and triggers an inbound route refresh to ensure that the routing table is up to date. Any prefixes in a BGP update that are treat-as-withdraw are removed from the BGP routing table.

This command is also supported for BGP template peers and BGP template peer sessions.

Discarding Path Attributes from a BGP Update Message

To discard BGP updates that contain specific path attributes, use the following command in router neighbor configuration mode:

Procedure

Command or Action Purpose

[no] path-attribute discard [value | range start end] in

Example:

switch#(config-router)# neighbor 10.20.30.40
switch(config-router-neighbor)# path-attribute discard 100 in

Example:

switch#(config-router)# neighbor 10.20.30.40
switch(config-router-neighbor)# path-attribute discard range 100 255 in

Drops specified path attributes in BGP update messages for the specified neighbor and triggers an inbound route refresh to ensure that the routing table is up to date. You can configure a specific attribute or an entire range of unwanted attributes.

This command is also supported for BGP template peers and BGP template peer sessions.

Note

When the same path attribute is configured for both discard and treat-as-withdaw, treat-as-withdraw has a higher priority.

Enabling or Disabling Enhanced Attribute Error Handling

BGP enhanced attribute error handling is enabled by default but can be disabled. This feature, which complies with RFC 7606, prevents peer sessions from flapping due to a malformed update. The default behavior applies to both eBGP and iBGP peers.

To disable or reenable enhanced error handling, use the following command in router configuration mode:

Procedure

Command or Action Purpose

Command or Action	Purpose
[no] enhanced-error Example: `switch(config)# router bgp 1000 switch(config-router)# enhanced-error`	Enables or disables BGP enhanced attribute error handling.

[no] enhanced-error

Example:

switch(config)# router bgp 1000
switch(config-router)# enhanced-error

Enables or disables BGP enhanced attribute error handling.

Displaying Discarded or Unknown Path Attributes

To display information about discarded or unknown path attributes, perform one of the following tasks:


Command	Purpose
show bgp {ipv4 \| ipv6} unicast path-attribute discard]	Displays all prefixes for which an attribute has been discarded.
show bgp {ipv4 \| ipv6} unicast path-attribute unknown]	Displays all prefixes that have an unknown attribute.
show bgp {ipv4 \| ipv6} unicast `ip-address`	Displays the unknown attributes and discarded attributes associated with a prefix.

The following example shows the prefixes for which an attribute has been discarded:

switch# show bgp ipv4 unicast path-attribute discard
Network            Next Hop
1.1.1.1/32         20.1.1.1
1.1.1.2/32         20.1.1.1
1.1.1.3/32         20.1.1.1

The following example shows the prefixes that have an unknown attribute:

switch# show bgp ipv4 unicast path-attribute unknown
Network            Next Hop
2.2.2.2/32         20.1.1.1
2.2.2.3/32         20.1.1.1

The following example shows the unknown attributes and discarded attributes associated with a prefix:

switch# show bgp ipv4 unicast 2.2.2.2
BGP routing table entry for 2.2.2.2/32, version 6241
Paths: (1 available, best #1, table default)
  Not advertised to any peer
  Refresh Epoch 1
  1000
    20.1.1.1 from 20.1.1.1 (20.1.1.1)
      Origin IGP, localpref 100, valid, external, best
      unknown transitive attribute: flag 0xE0 type 0x62 length 0x64
        value 0000 0000 0100 0000 0200 0000 0300 0000
              0400 0000 0500 0000 0600 0000 0700 0000
              0800 0000 0900 0000 0A00 0000 0B00 0000
              0C00 0000 0D00 0000 0E00 0000 0F00 0000
              1000 0000 1100 0000 1200 0000 1300 0000
              1400 0000 1500 0000 1600 0000 1700 0000
              1800 0000
      rx pathid: 0, tx pathid: 0x0
      Updated on Jul 20 2019 07:50:43 PST

Configuring AS Confederations

To configure an AS confederation, you must specify a confederation identifier. The group of autonomous systems within the AS confederation looks like a single autonomous system with the confederation identifier as the autonomous system number.

To configure a BGP confederation identifier, use the following command in router configuration mode:


Command	Purpose
confederation identifier `as-number` Example : `switch(config-router)# confederation identifier 64512`	Configures a confederation identifier for an AS confederation. Each confederation has a different sub-AS number, usually a private one (from 64512 to 65534). This command triggers an automatic notification and session reset for the BGP neighbor sessions.

To configure the autonomous systems that belong to the AS confederation, use the following command in router configuration mode:


Command	Purpose
bgp confederation peers `as-number` [ `as-number2`... ] Example : `switch(config-router)# bgp confederation peers 5 33 44`	Specifies a list of autonomous systems that belong to the confederation. This command triggers an automatic notification and session reset for the BGP neighbor sessions.

Configuring an Autonomous System Path Containing Your Own Autonomous System

Enable the feature for BGP to accept the autonomous system (AS) path that contains your own AS.

Before you begin

Ensure that you have enabled the BGP feature (see the Enabling the BGP Feature section).

SUMMARY STEPS

configure terminal
router bgp as-number
neighbor ip-address remote-as as-number
address-family ipv4 unicast
[ no | default ] allowas-in [allowas-in-cnt]
end
(Optional) show running-config bgp
(Optional) copy running-config startup-config

DETAILED STEPS

	Command or Action	Purpose
Step 1	configure terminal Example: `switch# configure terminal switch(config)#`	Enters configuration mode.
Step 2	router bgp `as-number` Example: `switch(config)# router bgp as-number`	Enters BGP mode and assigns the autonomous system number to the local BGP speaker. The `as-number` value range is from 1 to 65535.
Step 3	neighbor `ip-address` remote-as `as-number` Example: `switch(config-router)# neighbor 192.168.1.2 remote-as 65536 switch(config-router-neighbor)#`	Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address.
Step 4	address-family ipv4 unicast Example: `switch(config-router-neighbor)# address-family ipv4 unicast switch(config-router-neighbor-af)#`	Enters router address family configuration for the specified address family.
Step 5	[ no \| default ] allowas-in [`allowas-in-cnt`] Example: `switch(config-router-neighbor-af)# allowas-in 5`	Enables the allowas-in feature for BGP and configures the number of occurrences of the AS number. For `allowas-in-cnt` ,enter an integer between 1 and 10. By default, the number of occurrences of the AS number is set to 3.
Step 6	end Example: `switch(config-router-neighbor-af)# end`	Exits router address family configuration mode.
Step 7	(Optional) show running-config bgp Example: `switch# show running-config bgp`	(Optional) Displays the BGP configuration.
Step 8	(Optional) copy running-config startup-config Example: `switch(config-router-neighbor)# copy running-config startup-config`	(Optional) Saves this configuration change.

Example

This example shows how to configure the allowas-in feature for BGP and configure it for a unicast IPv4 address family:

switch# configure terminal
switch(config)# router bgp 77
switch(config-router)# neighbor 6.20.1.1 remote-as 66
switch(config-router-neighbor)# address-family ipv4 unicast
switch(config-router-neighbor-af)# allowas-in 5
switch(config-router-neighbor-af)# end

Configuring Route Reflector

You can configure iBGP peers as route reflector clients to the local BGP speaker, which acts as the 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 router ID of the route reflector. To increase redundancy and avoid a single point of failure in the network, you can configure a cluster with more than one route reflector. You must configure all route reflectors in the cluster with the same 4-byte cluster ID so that a route reflector can recognize updates from route reflectors in the same cluster.

Before you begin

Ensure that you have enabled the BGP feature (see the Enabling the BGP Feature section).

SUMMARY STEPS

configure terminal
router bgp as-number
cluster-id cluster-id
address-family ipv4 unicast
(Optional) client-to-client reflection
exit
neighbor ip-address remote-as as-number
address-family ipv4 unicast
route-reflector-client
show bgp ip unicast neighbors
(Optional) copy running-config startup-config

DETAILED STEPS

	Command or Action	Purpose
Step 1	configure terminal Example: `switch# configure terminal switch(config)#`	Enters configuration mode.
Step 2	router bgp `as-number` Example: `switch(config)# router bgp 65536 switch(config-router)#`	Enables BGP and assigns the autonomous system number to the local BGP speaker.
Step 3	cluster-id `cluster-id` Example: `switch(config-router)# cluster-id 192.0.2.1`	Configures the local router as one of the route reflectors that serve the cluster. You specify a cluster ID to identify the cluster. This command triggers an automatic soft clear or refresh of BGP neighbor sessions.
Step 4	address-family ipv4 unicast Example: `switch(config-router-neighbor)# address-family ipv4 unicast switch(config-router-neighbor-af)#`	Enters router address family configuration mode for the specified address family.
Step 5	(Optional) client-to-client reflection Example: `switch(config-router-af)# client-to-client reflection`	(Optional) Configures client-to-client route reflection. This feature is enabled by default. This command triggers an automatic soft clear or refresh of BGP neighbor sessions.
Step 6	exit Example: `switch(config-router-neighbor-af)# exit switch(config-router-neighbor)#`	Exits router address configuration mode.
Step 7	neighbor `ip-address` remote-as `as-number` Example: `switch(config-router)# neighbor 192.168.1.2 remote-as 65536 switch(config-router-neighbor)#`	Configures the IP address and AS number for a remote BGP peer.
Step 8	address-family ipv4 unicast Example: `switch(config-router-neighbor)# address-family ipv4 unicast switch(config-router-neighbor-af)#`	Enters neighbor address family configuration mode for the specified address family.
Step 9	route-reflector-client Example: `switch(config-router-neighbor-af)# route-reflector-client`	Configures the switch as a BGP route reflector and configures the neighbor as its client. This command triggers an automatic notification and session reset for the BGP neighbor sessions.
Step 10	show bgp ip unicast neighbors Example: `switch(config-router-neighbor-af)# show bgp ip unicast neighbors`	Displays the BGP peers.
Step 11	(Optional) copy running-config startup-config Example: `switch(config-router-neighbor)# copy running-config startup-config`	(Optional) Saves this configuration change.

Example

This example shows how to configure the router as a route reflector and add one neighbor as a client:

switch(config)# router bgp 65536
switch(config-router)# neighbor 192.0.2.10 remote-as 65536
switch(config-router-neighbor)# address-family ip unicast
switch(config-router-neighbor-af)# route-reflector-client
switch(config-router-neighbor-af)# copy running-config startup-config

Configuring Route Dampening

You can configure route dampening to minimize route flaps propagating through your iBGP network.

To configure route dampening, use the following command in address-family or VRF address family configuration mode:


Command	Purpose
dampening [{ `half-life reuse-limit suppress-limit max-suppress-time` \| route-map `map-name` }] Example : `switch(config-router-af)# dampening route-map bgpDamp`	Disables capabilities negotiation. The parameter values are as follows: half-life—The range is from 1 to 45. reuse-limit—The range is from 1 to 20000. suppress-limit—The range is from 1 to 20000 max-suppress-time—The range is from 1 to 255.

Configuring Load Sharing and ECMP

You can configure the maximum number of paths that BGP adds to the route table for equal-cost multipath load balancing.

Note

ECMP is not supported on warp mode.

To configure the maximum number of paths, use the following command in router address-family configuration mode:

Command

Purpose

maximum-paths [ ibgp ] maxpaths

Example :

switch(config-router-af)# maximum-paths 12

Configures the maximum number of equal-cost paths for load sharing. The range is from 1 to 32. The default is 1.

Note

It is recommended you set the maximum-path to 1 in warp mode to prevent ECMP configuration.

Configuring Maximum Prefixes

You can configure the maximum number of prefixes that BGP can receive from a BGP peer. If the number of prefixes exceeds this value, you can optionally configure BGP to generate a warning message or tear down the BGP session to the peer.

To configure the maximum allowed prefixes for a BGP peer, use the following command in neighbor address-family configuration mode:


Command	Purpose
maximum-prefix `maximum` [ `threshold` ] [ restart `time` \| warming-only ] Example : `switch(config-router-neighbor-af)# maximum-prefix 12`	Configures the maximum number of prefixes from a peer. The parameter ranges are as follows: `maximum` —The range is from 1 to 300000 `Threshold` —The range is from 1 to 100 percent. The default is 75 percent. `time` —The range is from 1 to 65535 minutes. This command triggers an automatic notification and session reset for the BGP neighbor sessions if the prefix limit is exceeded.

Configuring Dynamic Capability

You can configure dynamic capability for a BGP peer.

To configure dynamic capability, use the following command in neighbor configuration mode:


Command	Purpose
dynamic-capability Example : `switch(config-router-neighbor)# dynamic-capability`	Enables dynamic capability. This command triggers an automatic notification and session reset for the BGP neighbor sessions. This command is disabled by default.

Configuring Aggregate Addresses

You can configure aggregate address entries in the BGP route table.

To configure an aggregate address, use the following command in router address-family configuration mode:


Command	Purpose
aggregate-address `ip-prefix/length` [ as-set ] [ summary-only ] [ advertise-map `map-name` ] [ attribute-map `map-name` ] [ suppress-map `map-name` ] Example : `switch(config-router-af)# aggregate-address 192.0.2.0/8 as-set`	Creates an aggregate address. The path advertised for this route is an autonomous system set that consists 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 summary-only keyword filters all more specific routes from updates. The advertise-map keyword and argument specify the route map used to select attribute information from selected routes. The attribute-map keyword and argument specify the route map used to select attribute information from the aggregate. The suppress-map keyword and argument conditionally filters more specific routes.

Configuring BGP Conditional Advertisement

You can configure BGP conditional advertisement to limit the routes that BGP propagates. You define the following two route maps:

Advertise map—Specifies the conditions that the route must match before BGP considers the conditional advertisement. This route map can contain any appropriate match statements.
Exist map or nonexist map—Defines the prefix that must exist in the BGP table before BGP propagates a route that matches the advertise map. The nonexist map defines the prefix that must not exist in the BGP table before BGP propagates a route that matches the advertise map. BGP processes only the permit statements in the prefix list match statements in these route maps.

If the route does not pass the condition, BGP withdraws the route if it exists in the BGP table.

Before you begin

Ensure that you have enabled the BGP feature (see the Enabling the BGP Feature section).

SUMMARY STEPS

configure terminal
router bgp as-number
neighbor ip-address remote-as as-number
address-family ipv4 unicast
advertise-map adv-map { exist-map exist-rmap | non-exist-map nonexist-rmap }
(Optional) show ip bgp neighbor
(Optional) copy running-config startup-config

DETAILED STEPS

	Command or Action	Purpose
Step 1	configure terminal Example: `switch# configure terminal switch(config)#`	Enters configuration mode.
Step 2	router bgp `as-number` Example: `switch(config)# router bgp 65536 switch(config-router)#`	Enters BGP mode and assigns the autonomous system number to the local BGP speaker.
Step 3	neighbor `ip-address` remote-as `as-number` Example: `switch(config-router)# neighbor 192.168.1.2 remote-as 65537 switch(config-router-neighbor)#`	Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address.
Step 4	address-family ipv4 unicast Example: `switch(config-router-neighbor)# address-family ipv4 unicast switch(config-router-neighbor-af)#`	Enters address family configuration mode.
Step 5	advertise-map `adv-map` { exist-map `exist-rmap` \| non-exist-map `nonexist-rmap` } Example: `switch(config-router-neighbor-af)# advertise-map advertise exist-map exist`	Configures BGP to conditionally advertise routes based on the two configured route maps: `adv-map` —Specifies a route map with match statements that the route must pass before BGP passes the route to the next route map. The adv-map is a case-sensitive, alphanumeric string up to 63 characters. `exist-rmap` —Specifies a route map with match statements for a prefix list. A prefix in the BGP table must match a prefix in the prefix list before BGP will advertise the route. The exist-rmap is a case-sensitive, alphanumeric string up to 63 characters. `nonexist-rmap` —Specifies a route map with match statements for a prefix list. A prefix in the BGP table must not match a prefix in the prefix list before BGP will advertise the route. The nonexist-rmap is a case-sensitive, alphanumeric string up to 63 characters.
Step 6	(Optional) show ip bgp neighbor Example: `switch(config-router-neighbor-af)# show ip bgp neighbor`	(Optional) Displays information about BGP and the configured conditional advertisement route maps.
Step 7	(Optional) copy running-config startup-config Example: `switch(config-router-neighbor)# copy running-config startup-config`	(Optional) Saves this configuration change.

Example

This example shows how to configure BGP conditional advertisement:

switch# configure terminal
switch(config)# router bgp 65536
switch(config-router)# neighbor 192.0.2.2 remote-as 65537
switch(config-router-neighbor)# address-family ipv4 unicast
switch(config-router-neighbor-af)# advertise-map advertise exist-map exist
switch(config-router-neighbor-af)# exit
switch(config-router-neighbor)# exit
switch(config-router)# exit
switch(config)# route-map advertise
switch(config-route-map)# match as-path pathList
switch(config-route-map)# exit
switch(config)# route-map exit
switch(config-route-map)# match ip address prefix-list plist
switch(config-route-map)# exit
switch(config)# ip prefix-list plist permit 209.165.201.0/27

Configuring Route Redistribution

You can configure BGP to accept routing information from another routing protocol and redistribute that information through the BGP network. Optionally, you can assign a default route for redistributed routes.

Before you begin

Ensure that you have enabled the BGP feature (see the Enabling the BGP Feature section).

SUMMARY STEPS

configure terminal
router bgp as-number
address-family ipv4 unicast
redistribute { direct | { eigrp | ospf | ospfv3 | rip } instance-tag | static } route-map map-name
(Optional) default-metric value
(Optional) copy running-config startup-config

DETAILED STEPS

	Command or Action	Purpose
Step 1	configure terminal Example: `switch# configure terminal switch(config)#`	Enters configuration mode.
Step 2	router bgp `as-number` Example: `switch(config)# router bgp 65536 switch(config-router)#`	Enters BGP mode and assigns the autonomous system number to the local BGP speaker.
Step 3	address-family ipv4 unicast Example: `switch(config-router-neighbor)# address-family ipv4 unicast switch(config-router-neighbor-af)#`	Enters address family configuration mode.
Step 4	redistribute { direct \| { eigrp \| ospf \| ospfv3 \| rip } `instance-tag` \| static } route-map `map-name` Example: `switch(config-router-af)# redistribute eigrp 201 route-map Eigrpmap`	Redistributes routes from other protocols into BGP. See the Configuring Route Maps section for more information about route maps.
Step 5	(Optional) default-metric `value` Example: `switch(config-router-af)# default-metric 33`	(Optional) Generates a default route into BGP.
Step 6	(Optional) copy running-config startup-config Example: `switch(config-router-neighbor)# copy running-config startup-config`	(Optional) Saves this configuration change.

Example

This example shows how to redistribute EIGRP into BGP:

switch# configure terminal
switch(config)# router bgp 65536
switch(config-router)# address-family ipv4 unicast
switch(config-router-af)# redistribute eigrp 201 route-map Eigrpmap
switch(config-router-af)# copy running-config startup-config

Configuring Multiprotocol BGP

You can configure MP-BGP to support multiple address families, including IPv4unicast routes.

Before you begin

Ensure that you have enabled the BGP feature (see the Enabling the BGP Feature section).

SUMMARY STEPS

configure terminal
router bgp as-number
neighbor ip-address remote-as as-number
address-family ipv4 unicast
(Optional) copy running-config startup-config

DETAILED STEPS

	Command or Action	Purpose
Step 1	configure terminal Example: `switch# configure terminal switch(config)#`	Enters configuration mode.
Step 2	router bgp `as-number` Example: `switch(config)# router bgp 65536 switch(config-router)#`	Enters BGP mode and assigns the autonomous system number to the local BGP speaker.
Step 3	neighbor `ip-address` remote-as `as-number` Example: `switch(config-router)# neighbor 192.168.1.2 remote-as 65537 switch(config-router-neighbor)#`	Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address.
Step 4	address-family ipv4 unicast Example: `switch(config-router-neighbor)# address-family ipv4 unicast switch(config-router-neighbor-af)#`	Enters address family configuration mode.
Step 5	(Optional) copy running-config startup-config Example: `switch(config-router-neighbor)# copy running-config startup-config`	(Optional) Saves this configuration change.

Tuning BGP

You can tune BGP characteristics through a series of optional parameters.

To tune BGB, use the following optional commands in router configuration mode:


Command	Purpose
bestpath [ always-compare-med \| compare-routerid \| med { missing-as-worst \| non-deterministic } \| as-path multipath-relax ] Example : `switch(config-router)# bestpath always-compare-med` `switch(config-router)# bestpath as-path multipath-relax`	Modifies the best-path algorithm. The optional parameters are as follows: always-compare-med —Compares MED on paths from different autonomous systems. compare-routerid —Compares the router IDs for identical eBGP paths. med missing-as-worst —Handles a missing MED as the highest MED. med non-deterministic —Does not always select the best MED path from among the paths from the same autonomous systems. as-path multipath-relax —Allows the switch to handle the paths received from different autonomous systems for multipath, if their AS-path lengths are the same and other multipath conditions are met.
enforce-first-as Example: `switch(config-router)# enforce-first-as`	Enforces the neighbor autonomous system to be the first AS number listed in the AS_path attribute for eBGP.
log-neighbor-changes Example : `switch(config-router)# log-neighbor-changes`	Generates a system message when a neighbor changes state.
router-id `id` Example : `switch(config-router)# router-id 209.165.20.1`	Manually configures the router ID for this BGP speaker.
timers [ bestpath-delay `delay` \| bgp `keepalive holdtime` \| prefix-peer-timeout `timeout` ] Example : `switch(config-router)# timers bgp 90 270`	Sets the BGP timer values. The optional parameters are as follows: You must manually reset the BGP sessions after configuring this command.

To tune BGP, use the following optional command in router address-family configuration mode:


Command	Purpose
distance `ebgp-distance ibgp distance local-distance` Example : `switch(config-router-af)# distance 20 100 200`	Sets the administrative distance for BGP. The range is from 1 to 255. The defaults are as follows:

To tune BGP, use the following optional commands in neighbor configuration mode:


Command	Purpose
description `string` Example : `switch(config-router-neighbor)# description main site`	Sets a descriptive string for this BGP peer. The string can be up to 80 alphanumeric characters.
low-memory exempt Example : `switch(config-router-neighbor)# low-memory exempt`	Exempts this BGP neighbor from a possible shutdown due to a low memory condition.
transport connection-mode passive Example: `switch(config-router-neighbor)# transport connection-mode passive`	Allows a passive connection setup only. This BGP speaker does not initiate a TCP connection to a BGP peer. You must manually reset the BGP sessions after configuring this command.
remove-private-as Example : `switch(config-router-neighbor)# remove-private-as`	Removes private AS numbers from outbound route updates to an eBGP peer. This command triggers an automatic soft clear or refresh of BGP neighbor sessions.
update-source `interface-type number` Example : `switch(config-router-neighbor)# update-source ethernet 2/1`	Configures the BGP speaker to use the source IP address of the configured interface for BGP sessions to the peer. This command triggers an automatic notification and session reset for the BGP neighbor sessions.

To tune BGP, use the following optional commands in neighbor address-family configuration mode:


Command	Purpose
suppress-inactive Example : `switch(config-router-neighbor-af)# suppress-inactive`	Advertises the best (active) routes only to the BGP peer. This command triggers an automatic soft clear or refresh of BGP neighbor sessions.
default-originate [ route-map `map-name` ] Example : switch(config-router-neighbor-af)# default-originate	Generates a default route to the BGP peer.
filter-list `list-name` { in \| out } Example: `switch(config-router-neighbor-af)# filter-list BGPFilter in`	Applies an AS_path filter list to this BGP peer for inbound or outbound route updates. This command triggers an automatic soft clear or refresh of BGP neighbor sessions.
prefix-list `list-name` { in \| out } Example: `switch(config-router-neighbor-af)# prefix-list PrefixFilter in`	Applies a prefix list to this BGP peer for inbound or outbound route updates. This command triggers an automatic soft clear or refresh of BGP neighbor sessions.
send-community Example : `switch(config-router-neighbor-af)# send-community`	Sends the community attribute to this BGP peer. This command triggers an automatic soft clear or refresh of BGP neighbor sessions.
send-extcommunity Example : `switch(config-router-neighbor-af)# send-extcommunity`	Sends the extended community attribute to this BGP peer. This command triggers an automatic soft clear or refresh of BGP neighbor sessions.

Configuring Virtualization

Before you begin

Ensure that you have enabled the BGP feature (see the Enabling the BGP Feature section).

SUMMARY STEPS

configure terminal
vrf context vrf-name
exit
router bgp as-number
vrf vrf-name
neighbor ip-address remote-as as-number
(Optional) bestpath as-path multipath-relax
(Optional) copy running-config startup-config

DETAILED STEPS

	Command or Action	Purpose
Step 1	configure terminal Example: `switch# configure terminal switch(config)#`	Enters configuration mode.
Step 2	vrf context `vrf-name` Example: `switch(config)# vrf context RemoteOfficeVRF switch(config-vrf)#`	Creates a new VRF and enters VRF configuration mode.
Step 3	exit Example: `switch(config-vrf)# exit switch(config)#`	Exits VRF configuration mode.
Step 4	router bgp `as-number` Example: `switch(config)# router bgp 65536 switch(config-router)#`	Creates a new BGP process with the configured autonomous system number.
Step 5	vrf `vrf-name` Example: `switch(config-router)# vrf RemoteOfficeVRF switch(config-router-vrf)#`	Enters the router VRF configuration mode and associates this BGP instance with a VRF.
Step 6	neighbor `ip-address` remote-as `as-number` Example: `switch(config-router-vrf)# neighbor 209.165.201.1 remote-as 65536 switch(config-router--vrf-neighbor)#`	Configures the IP address and AS number for a remote BGP peer.
Step 7	(Optional) bestpath as-path multipath-relax Example: `switch(config-router-vrf)# bestpath as-path multipath-relax`	(Optional) Allows the switch to treat paths received from different autonomous systems for multipath, if their autonomous path lengths are the same and other multipath conditions are met.
Step 8	(Optional) copy running-config startup-config Example: `switch(config-router-neighbor)# copy running-config startup-config`	(Optional) Saves this configuration change.

Example

This example shows how to create a VRF and configure the router ID in the VRF:

switch# configure terminal
switch(config)# vrf context NewVRF
switch(config-vrf)# exit
switch(config)# router bgp 65536
switch(config-router)# vrf NewVRF
switch(config-router-vrf)# neighbor 209.165.201.1 remote-as 65536
switch(config-router-vrf-neighbor)# copy running-config startup-config

About BGP Graceful Shutdown

Beginning with release 9.3(1), BGP supports the graceful shutdown feature. This BGP feature works with the BGP shutdown command. Despite the name, BGP graceful shutdown does not actually cause a shutdown. Instead, it alerts connected routers that a router or link will be going down soon.

Dramatically decrease the network convergence time when a router or link is taken offline.
Reduce or eliminate dropped packets that are in transit when a router or link is taken offline.

The graceful shutdown feature uses the GRACEFUL_SHUTDOWN well-known community (0xFFFF0000 or 65535:0), which is identified by IANA and the IETF through RFC 8326. This well-known community can be attached to any routes, and it is processed like any other attribute of a route.

Because this feature announces that a router or link will be going down, the feature is useful in preparation of maintenance windows or planned outages. Use this feature before shutting down BGP to limit the impact on traffic.

Graceful Shutdown Aware and Activate

BGP routers can control the preference of all routes with the GRACEFUL_SHUTDOWN community through the concept of GRACEFUL SHUTDOWN awareness. Graceful shutdown awareness is enabled by default, which enables the receiving peers to deprefer incoming routes carrying the GRACEFUL_SHUTDOWN community. Although not a typical use case, you can disable and reenable graceful shutdown awareness through the graceful-shutdown aware command.

Graceful shutdown aware is applicable only at the BGP global context. For information about contexts, see Graceful Shutdown Contexts. The aware option operates with another option, the activate option, which you can assign to a route map for more granular control over graceful shutdown routes.

Interaction of the Graceful Shutdown Aware and Activate Options

When a graceful shutdown is activated, the GRACEFUL_SHUTDOWN community is appended to route updates only when you specify the activate keyword. At this point, new route updates that contain the community are generated and transmitted. When the graceful-shutdown aware command is configured, all routers that receive the community then deprefer (lower the route preference of) the routes in the update. Without the graceful-shutdown aware command, BGP does not deprefer routes with the GRACEFUL_SHUTDOWN community.

After the feature is activated and the routers are aware of graceful shutdown, BGP still considers the routes with the GRACEFUL_SHUTDOWN community as valid. However, those routes are given the lowest priority in the best-path calculation. If alternate paths are available, new best paths are chosen, and convergence occurs to accommodate the router or link that will soon go down.

Graceful Shutdown Contexts

BGP graceful shutdown feature has two contexts that determine what the feature affects and what functionality is available.


Context	Affects	Commands
Global	The entire switch and all routes processed by it. For example, readvertise all routes with the GRACEFUL_SHUTDOWN community.	graceful-shutdown activate [route-map `route-map`] graceful-shutdown aware
Peer	A BGP peer or a link between neighbors. For example, advertise only one link between peers with GRACEFUL_SHUTDOWN community.	graceful-shutdown activate [route-map `route-map`]

Graceful Shutdown with Route Maps

Graceful shutdown works with the route policy manager (RPM) feature to control how the switch's BGP router transmits and receives routes with the GRACEFUL_SHUTDOWN community. Route maps can process route updates with the community in the inbound and outbound directions. Typically, route maps are not required. However, if needed, you can use them to customize the control of graceful shutdown routes.

Normal Inbound Route Maps

Normal inbound route maps affect routes that are incoming to the BGP router. Normal inbound route maps are not commonly used with the graceful shutdown feature because routers are aware of graceful shutdown by default.

Cisco Nexus switches running Cisco NX-OS Release 9.3(1) and later do not require an inbound route map for the graceful shutdown feature. Cisco NX-OS Release 9.3(1) and later have implicit inbound route maps that automatically deprefer any routes that have the GRACEFUL_SHUTDOWN community if the BGP router is graceful shutdown aware.

Normal inbound route maps can be configured to match against the well-known GRACEFUL_SHUTDOWN community. Although these inbound route maps are not common, there are some cases where they are used:

If switches are running a Cisco NX-OS release earlier than 9.3(1), they do not have the implicit inbound route map present in NX-OS 9.3(1). To use the graceful shutdown feature on these switches, you must create a graceful shutdown inbound route map. The route map must match inbound routes with the well-known GRACEFUL_SHUTDOWN community, permit them, and deprefer them. If an inbound route map is needed, create it on the BGP peer that is running a version of NX-OS earlier than 9.3(1) and is receiving the graceful shutdown routes.
If you want to disable graceful shutdown aware, but still want the router to act on incoming routes with GRACEFUL_SHUTDOWN community from some BGP neighbors, you can configure an inbound route map under the respective peers.

Normal Outbound Route Maps

Normal outbound route maps control forwarding the routes that a BGP router sends. Normal outbound route maps can affect the graceful shutdown feature. For example, you can configure an outbound route map to match on the GRACEFUL_SHUTDOWN community and set attributes, and it takes precedence over any graceful shutdown outbound route maps.

Graceful Shutdown Outbound Route Maps

Outbound Graceful shutdown route maps are specific type of outbound route map for the graceful shutdown feature. They are optional, but they are useful when you already have a community list that is associated with a route map. The typical graceful shutdown outbound route map contains only set clauses to set or modify certain attributes.

You can use outbound route maps in the following ways:

For customers that already have existing outbound route maps, you can add a new entry with a higher sequence number, match on the GRACEFUL_SHUTDOWN well-known community, and add any attributes that you want.
You can also use a graceful shutdown outbound route map with the graceful-shutdown activate route-map name option. This is the typical use case.

This route map requires no match clauses, so the route map matches on all routes being sent to the neighbor.

Route Map Precedence

When multiple route maps are present on the same router, the following order of precedence is applied to determine how routes with the community are processed:Consider the following example. Assume you have a standard outbound route map name Red that sets a local-preference of 60. Also, assume you have a peer graceful-shutdown route map that is named Blue that sets local-pref to 30. When the route update is processed, the local preference will be set to 60 because Red overwrites Blue.

Normal outbound route maps take precedence over peer graceful shutdown maps.
Peer graceful shutdown maps take precedence over global graceful shutdown maps.

Guidelines and Limitations

The following are limitations and guidelines for BGP global shutdown:

Graceful shutdown feature can only help avoid traffic loss when alternative routes exist in the network for the affected routers. If the router has no alternate routes, routes carrying the GRACEFUL_SHUTDOWN community are the only ones available, and therefore, are used in the best-path calculation. This situation defeats the purpose of the feature.
Configuring a BGP send community is required to send the GRACEFUL_SHUTDOWN community.
For route maps:
- When global route maps and neighbor route maps are configured, the per-neighbor route maps take precedence.
- Outbound route maps take precedence over any global route maps configured for graceful shutdown.
- Outbound route maps take precedence over any peer route maps configured for graceful shutdown.
- To add the graceful shutdown functionality to legacy (existing) inbound route maps, follow this order:
  1. Add the graceful shutdown match clause to the top of the route map by setting a low sequence number for the clause (for example, sequence number 0).
  2. Add a continue statement after the graceful shutdown clause. If you omit the continue statement, route-map processing stops when it matches the graceful shutdown clause, any other clauses with higher sequence numbers (for example, 1 and higher) are not processed.

Graceful Shutdown Task Overview

To use the graceful shutdown feature, you typically enable graceful-shutdown aware on all Cisco Nexus switches and leave the feature enabled. When a BGP router must be taken offline, you configure graceful-shutdown activate on it.

The following details document the best practice for using the graceful shutdown feature.

To bring the router or link down:

Configure the Graceful Shutdown feature.
Watch the neighbor for the best path.
When the best path is recalculated, issue the shutdown command to disable BGP.
Perform the work that required you to shut down the router or link.

To bring the router or link back online:

When you finish the work that required the shutdown, reenable BGP (no shutdown ).
Disable the graceful shutdown feature (no graceful-shutdown activate in config router mode).

Configuring Graceful Shutdown on a Link

This task enables you to configure graceful shutdown on a specific link between two BGP routers.

Before you begin

If you have not already enabled BGP, enable it now (feature bgp ).

SUMMARY STEPS

config terminal
router bgp autonomous-system-number
neighbor { ipv4-address|ipv6-address } remote-as as-number
graceful-shutdown activate [route-map map-name]

DETAILED STEPS

	Command or Action	Purpose
Step 1	config terminal Example: `switch-1# configure terminal switch-1(config)#`	Enters global configuration mode.
Step 2	router bgp `autonomous-system-number` Example: `switch-1(config)# router bgp 110 switch-1(config-router)#`	Enters router configuration mode to create or configure a BGP routing process.
Step 3	neighbor { `ipv4-address`\|`ipv6-address` } remote-as `as-number` Example: `switch-1(config-router)# neighbor 10.0.0.3 remote-as 200 switch-1(config-router-neighbor)#`	Configures the autonomous system (AS) to which the neighbor belongs.
Step 4	graceful-shutdown activate [route-map `map-name`] Example: `switch-1(config-router-neighbor)# graceful-shutdown activate route-map gshutPeer switch-1(config-router-neighbor)#`	Configures graceful shutdown on the link to the neighbor. Also, advertises the routes with the well-known GRACEFUL_SHUTDOWN community and applies the route map to the outbound route updates. The routes are advertised with the graceful-shutdown community by default. In this example, routes are advertised to the neighbor with the Graceful-shutdown community with a route-map named gshutPeer. The devices receiving the gshut community look at the communities of the route and optionally use the communities to apply routing policy.

Filtering BGP Routes and Setting Local Preference Based On GRACEFUL_SHUTDOWN Communities

Switches that are not yet running 9.3(1) do not have an inbound route map that matches against the GRACEFUL_SHUTDOWN community name. Therefore, they have no way of identifying and depreferring the correct routes.

For switches running a release of NX-OS that is earlier than 9.3(1), you must configure an inbound route map that matches on the community value for graceful shutdown (65535:0) and deprefers routes.

If your switch is running 9.3(1) or later, you do not need to configure an inbound route map.

SUMMARY STEPS

configure terminal
ip community list standard community-list-name seq sequence-number { permit | deny } value
route map map-tag {deny | permit} sequence-number
match community community-list-name
set local-preference local-pref-value
exit
router bgp community-list-name
neighbor { ipv4-address|ipv6-address }
address-family { address-family sub family }
send community
route map map-tag in

DETAILED STEPS

	Command or Action	Purpose
Step 1	configure terminal Example: `switch-1# configure terminal switch-1<config)#`	Enters global configuration mode.
Step 2	ip community list standard `community-list-name` seq `sequence-number` { permit \| deny } `value` Example: `switch-1(config)# ip community-list standard GSHUT seq 10 permit 65535:0 switch-1(config)#`	Configures a community list and permits or denies routes that have the well-known graceful shutdown community value.
Step 3	route map `map-tag` {deny \| permit} `sequence-number` Example: `switch-1(config)# route-map RM_GSHUT permit 10 switch-1(config-route-map)#`	Configures a route map as sequence 10 and permits routes that have the GRACEFUL_SHUTDOWN community.
Step 4	match community `community-list-name` Example: `switch-1(config-route-map)# match community GSHUT switch-1(config-route-map)#`	Configures that routes that match the IP community list GSHUT are processed by Route Policy Manager (RPM).
Step 5	set local-preference `local-pref-value` Example: `switch-1(config-route-map)# set local-preference 10 switch-1(config-route-map)#`	Configures that the routes that match the IP community list GSHUT will be given a specified local preference.
Step 6	exit Example: `switch-1(config-route-map)# exit switch-1(config)#`	Leaves route map configuration and returns to global configuration mode.
Step 7	router bgp `community-list-name` Example: `switch-1(config)# router bgp 100 switch-1(config-router)#`	Enters router configuration mode and creates a BGP instance.
Step 8	neighbor { `ipv4-address`\|`ipv6-address` } Example: `switch-1(config-router)# neighbor 10.0.0.3 switch-1(config-router-neighbor)#`	Enters route BGP neighbor mode for a specified neighbor.
Step 9	address-family { `address-family` `sub family` } Example: `nxosv2(config-router-neighbor)# address-family ipv4 unicast nxosv2(config-router-neighbor-af)#`	Puts the neighbor into address family (AF) configuration mode.
Step 10	send community Example: `nxosv2(config-router-neighbor-af)# send-community nxosv2(config-router-neighbor-af)#`	Enables BGP community exchange with the neighbor.
Step 11	route map `map-tag` in Example: `nxosv2(config-router-neighbor-af)# route-map RM_GSHUT in nxosv2(config-router-neighbor-af)#`	Applies the route map to incoming routes from the neighbor. In this example, the route map that is named RM_GSHUT permits routes with the GRACEFUL_SHUTDOWN community from the neighbor.

Configuring Graceful Shutdown for All BGP Neighbors

You can manually apply the GRACEFUL_SHUTDOWN well-known community to all the neighbors of a graceful shutdown initiator.

You can configure graceful shutdown at the global level for all BGP neighbors.

Before you begin

If you have not already enabled BGP, enable it now (feature bgp ).

SUMMARY STEPS

configure terminal
router bgp autonomous-system-number
graceful-shutdown activate [route-map map-name]

DETAILED STEPS

Command or Action Purpose

Step 1

configure terminal

Example:

switch-1# configure terminal
switch-1(config)#

Enters global configuration mode.

Step 2

router bgp autonomous-system-number

Example:

switch-1(config)# router bgp 110
switch-1(config-router)#

Enters router configuration mode to create or configure a BGP routing process.

Step 3

graceful-shutdown activate [route-map map-name]

Example:

switch-1(config-router-neighbor)# graceful-shutdown activate route-map gshutPeer
switch-1(config-router-neighbor)#

Configures graceful shutdown route map for the links to all neighbors. Also, advertises all routes with the well-known GRACEFUL_SHUTDOWN community and applies the route map to the outbound route updates.

The routes are advertised with the GRACEFUL_SHUTDOWN community by default. In this example, routes are advertised to all neighbors with the community with a route-map named gshutPeer. The route map should contain only set clauses.

The devices receiving the GRACEFUL_SHUTDOWN community look at the communities of the route and optionally use the communities to apply routing policy.

Controlling the Preference for All Routes with the GRACEFUL_SHUTDOWN Community

Cisco NX-OS enables lowering the preference of incoming routes that have the GRACEFUL_SHUTDOWN community. When graceful shutdown aware is enabled, BGP considers routes carrying the community as the lowest preference during best path calculation. By default, lowering the preference is enabled, but you can selectively disable this option.

Whenever you enable or disable this option, you trigger a BGP best-path calculation. This option gives you the flexibility to control the behavior of the BGP best-path calculation for the graceful shutdown well-known community.

Before you begin

If you have not enabled BGP, enable it now (feature bgp ).

SUMMARY STEPS

configure terminal
router bgp autonoums-system
(Optional) no graceful-shutdown aware

DETAILED STEPS

Command or Action Purpose

Step 1

configure terminal

Example:

switch-1(config)# config terminal
switch-1(config)#

Enters global configuration mode.

Step 2

router bgp autonoums-system

Example:

switch-1(config)# router bgp 100
switch-1(config-router)#

Enters router configuration mode and configures a BGP routing process.

Step 3

(Optional) no graceful-shutdown aware

Example:

switch-1(config-router)# no graceful-shutdown aware
switch-1(config-router)#

For this BGP router, do not give lower preference for all routes that have the GRACEFUL_SHUTDOWN community. The default action is to deprefer routes when the graceful shutdown aware feature is disabled, so using the no form of the command is optional for not depreferring graceful shutdown routes.

Preventing Sending the GRACEFUL_SHUTDOWN Community to a Peer

If you no longer need the GRACEFUL_SHUTDOWN community that is appended as a route attribute to outbound route updates, you can remove the community, which no longer sends it to a specified neighbor. One use case would be when a router is at an autonomous system boundary, and you do not want the graceful shutdown functionality to propagate outside of an autonomous system boundary.

To prevent sending the GRACEFUL_SHUTDOWN to a peer, you can disable the send community option or strip the community from the outbound route map.

Choose either of the following methods:

Disable the send-community in the running config.

Example:
```
nxosv2(config-router-neighbor-af)# no send-community standard 
nxosv2(config-router-neighbor-af)# 
```
If you use this option, the GRACEFUL_SHUTDOWN community is still received by the switch, but it is not sent to the downstream neighbor through the outbound route map. All standard communities are not sent either.
Delete the GRACEFUL_SHUTDOWN community through an outbound route map by following these steps:
1. Create an IP community list matches the GRACEFUL_SHUTDOWN community.
2. Create an outbound route map to match against the GRACEFUL_SHUTDOWN community.
3. Use a set community-list delete clause to strip GRACEFUL_SHUTDOWN community.
If you use this option, the community list matches and permits the GRACEFUL_SHUTDOWN community, then the outbound route map matches against the community and then deletes it from the outbound route map. All other communities pass through the outbound route map without issue.

Displaying Graceful Shutdown Information

Information about the graceful shutdown feature is available through the following show commands.


Command	Action
show ip bgp community-list graceful-shutdown	Shows all entires in the BGP routing table that have the GRACEFUL_SHUTDOWN community.
show running-config bgp	Shows the running BGP configuration.
show running-config bgp all	Shows all information for the running BGP configuration including information about the graceful shutdown feature.
show bgp `address-family` neighbors `neighbor-address`	When the feature is configured for the peer, shows the following: The state of the graceful-shutdown-activate feature for the specified neighbor The name of any graceful shutdown route map configured for the specified neighbor
show bgp process	Shows different information depending on the context. When the graceful-shutdown-activate option is configured in peer context, shows the enabled or disabled state for the feature through graceful-shutdown-active . When the graceful-shutdown-activate option is configured in global context and has a graceful-shutdown route map, shows the enabled state of the feature through the following: graceful-shutdown-active graceful-shutdown-aware graceful-shutdown route-map
show ip bgp `address`	For the specified address, shows the BGP routing table information, including the following: The state of the specified address as the best path Whether the specified address is part of the GRACEFUL_SHUTDOWN community

Graceful Shutdown Configuration Examples

These examples show some configurations for using the graceful shutdown feature.

Configuring Graceful Shutdown for a BGP Link

The following example shows how to configure graceful shutdown while setting a local preference and a community:

Configuring graceful shutdown activate for the link to the specified neighbor
Adding the GRACEFUL_SHUTDOWN community to the routes

Setting a route map named gshutPeer with only set clauses for outbound routes with the community.

router bgp 100
    neighbor 20.0.0.3 remote-as 200
         graceful-shutdown activate route-map gshutPeer 
         address-family ipv4 unicast
              send-community 

route-map gshutPeer permit 10
    set local-preference 0
    set community 200:30

Configuring Graceful Shutdown for All-Neighbor BGP Links

The following example shows:

Configuring graceful shutdown activate for all the links connecting the local router and all its neighbors.
Adding the GRACEFUL_SHUTDOWN community to the routes.
Setting a route map that is named gshutAall with only set clauses for all outbound routes.

router bgp 200
   graceful-shutdown activate route-map gshutAll

route-map gshutAll permit 10
   set as-path prepend 10 100 110
   set community 100:80

route-map Red permit 10
   set local-pref 20

router bgp 100
   graceful-shutdown activate route-map gshutAll 
      router-id 2.2.2.2  
         address-family ipv4 unicast
         network 2.2.2.2/32    
         neighbor 1.1.1.1 remote-as 100
         update-source loopback0
         address-family ipv4 unicast
            send-community 
         neighbor 20.0.0.3 remote-as 200
         address-family ipv4 unicast
            send-community 
               route-map Red out

In this example, the gshutAll route-map takes effect for neighbor 1.1.1.1, but not neighbor 20.0.0.3, because the outbound route-map Red configured under neighbor 20.0.0.3 takes precedence instead.

Configuring Graceful Shutdown Under a Peer-Template

This example configures the graceful shutdown feature under a peer-session template, which is inherited by a neighbor.

router bgp 200
   template peer-session p1
      graceful-shutdown activate route-map gshut_out
   neighbor 1.1.1.1 remote-as 100
      inherit peer-session p1
      address-family ipv4 unicast
         send-community

Filtering BGP Routes and Setting Local Preference Based on GRACEFUL_SHUTDOWN Community Using and Inbound Route Map

This example shows how to use a community list to filter the incoming routes that have the GRACEFUL_SHUTDOWN community. This configuration is useful for legacy switches that are not running Cisco NX-OS 9.3(1) as a minimum version.

The following example shows:

An IP Community List that permits routes that have the GRACEFUL_SHUTDOWN community.
A route map that is named RM_GSHUT that permits routes based on a standard community list named GSHUT.
The route map also sets the preference for the routes it processes to 0 so that those routes are given lower preference for best path calculation when the router goes offline. The route map is applied to incoming IPv4 routes from the neighbor (20.0.0.2).

ip community-list standard GSHUT permit 65535:0

route-map RM_GSHUT permit 10
   match community GSHUT
   set local-preference 0

router bgp 200
   neighbor 20.0.0.2 remote-as 100
      address-family ipv4 unicast
         send-community 
         route-map RM_GSHUT in

Verifying the Advanced BGP Configuration

To display the BGP configuration information, perform one of the following tasks:


Command	Purpose
show bgp all [summary] [vrf `vrf-name`]	Displays the BGP information for all address families.
show bgp convergence [vrf `vrf-name`]	Displays the BGP information for all address families.
show bgp ip {unicast} [`ip-address`] community {regexp `expression` \| [community] [no-advertise] [no-export] [no-export-subconfed]} [vrf `vrf-name`]	Displays the BGP routes that match a BGP community.
show bgp [vrf `vrf-name`] ip {unicast} [`ip-address`] community-list list-name [vrf `vrf-name`]	Displays the BGP routes that match a BGP community list.
show bgp ip {unicast} [`ip-address`] extcommunity {regexp `expression` \| generic [non-transitive \| transitive] `aa4:nn` [exact-match]} [vrf `vrf-name`]	Displays the BGP routes that match a BGP extended community.
show bgp ip {unicast} [ip-address] extcommunity-list `list-name` [exact-match] [vrf `vrf-name`]	Displays the BGP routes that match a BGP extended community list.
show bgp ip {unicast} [`ip-address`] {dampening `dampened-paths` [regexp `expression`]} [vrf `vrf-name`]	Displays the information for BGP route dampening. Use the clear bgp dampening command to clear the route flap dampening information.
show bgp ip {unicast} [`ip-address`] history-paths [regexp `expression`] [vrf `vrf-name`]	Displays the BGP route history paths.
show bgp ip {unicast} [`ip-address`] filter-list `list-name` [vrf `vrf-name`]	Displays the information for the BGP filter list.
show bgp ip {unicast} [`ip-address`] neighbors [`ip-address`] [vrf `vrf-name`]	Displays the information for BGP peers. Use the clear bgp neighbors command to clear these neighbors.
show bgp ip {unicast} [`ip-address`] {nexthop \| nexthop-database} [vrf `vrf-name`]	Displays the information for the BGP route next hop.
show bgp paths	Displays the BGP path information.
show bgp ip {unicast} [`ip-address`] policy name [vrf `vrf-name`]	Displays the BGP policy information. Use the clear bgp policy command to clear the policy information.
show bgp ip {unicast} [`ip-address`] prefix-list `list-name` [vrf `vrf-name`]	Displays the BGP routes that match the prefix list.
show bgp ip {unicast} [`ip-address`] received-paths [vrf `vrf-name`]	Displays the BGP paths stored for soft reconfiguration.
show bgp ip {unicast} [`ip-address`] regexp `expression` [vrf `vrf-name`]	Displays the BGP routes that match the AS_path regular expression.
show bgp ip {unicast} [`ip-address`] route-map `map-name` [vrf `vrf-name`]	Displays the BGP routes that match the route map.
show bgp peer-policy `name` [ vrf `vrf-name` ]	Displays the information about BGP peer policies.
show bgp peer-session `name` [ vrf `vrf-name` ]	Displays the information about BGP peer sessions.
show bgp peer-template `name` [ vrf `vrf-name` ]	Displays the information about BGP peer templates. Use the clear bgp peer-template command to clear all neighbors in a peer template.
show bgp process	Displays the BGP process information.
show ip bgp `options`	Displays the BGP status and configuration information. This command has multiple options. See the Cisco Nexus 3000 Series Command Reference for more information.
show ip mbgp `options`	Displays the BGP status and configuration information. This command has multiple options. See the Cisco Nexus 3000 Series Command Reference for more information.
show running-configuration bgp	Displays the current running BGP configuration.

Displaying BGP Statistics

To display BGP statistics, use the following commands:


Command	Purpose
show bgp ip {unicast} [`ip-address`] flap-statistics [vrf `vrf-name`]	Displays the BGP route flap statistics. Use the clear bgp flap-statistics command to clear these statistics.
show bgp sessions [vrf `vrf-name`]	Displays the BGP sessions for all peers. Use the clear bgp sessions command to clear these statistics.
show bgp sessions [vrf `vrf-name`]	Displays the BGP sessions for all peers. Use the clear bgp sessions command to clear these statistics.
show bgp statistics	Displays the BGP statistics.

Additional References

For additional information related to implementing BGP, see the following sections:

Related Documents
MIBs

MIBs


MIBs	MIBs Link
BGP4-MIB CISCO-BGP4-MIB	To locate and download MIBs, go to the following: MIB Locator.

Bias-Free Language

Results

Chapter: Configuring Advanced BGP

Configuring Advanced BGP

Information About Advanced BGP

Peer Templates

Authentication

Route Policies and Resetting BGP Sessions

eBGP

iBGP

AS Confederations

Route Reflector

Capabilities Negotiation

Route Dampening

Load Sharing and Multipath

Route Aggregation

BGP Conditional Advertisement

BGP Next-Hop Address Tracking

Route Redistribution

Tuning BGP

BGP Timers

Tuning the Best-Path Algorithm

Multiprotocol BGP

Prerequisites for BGP

Guidelines and Limitations for Advanced BGP

Default Settings for BGP

Configuring Advanced BGP

Configuring BGP Session Templates

Before you begin

SUMMARY STEPS

DETAILED STEPS

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Configuring BGP Peer-Policy Templates

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Configuring BGP Peer Templates

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Configuring BGP Interface Peering via IPv6 Link-Local for IPv4 and IPv6 Address Families