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MPLS VPN—Explicit Null Label Support with BGP IPv4 Label Session

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MPLS VPN—Explicit Null Label Support with BGP IPv4 Label Session

Finding Feature Information

Contents

Prerequisites for MPLS—VPN Explicit Null Label Support with BGP IPv4 Label Session

Restrictions for MPLS—VPN Explicit Null Label Support with BGP IPv4 Label Session

Information About MPLS—VPN Explicit Null Label Support with BGP IPv4 Label Session

Feature Design of the MPLS—VPN Explicit Null Label Support with BGP IPv4 Label Session Feature

Benefits of the MPLS—VPN Explicit Null Label Support BGP IPv4 Label Session Feature

How to Configure MPLS—VPN Explicit Null Label Support with BGP IPv4 Label Session

Configuring CSC with BGP

Verifying Explicit Null Configuration

Configuration Examples for MPLS—VPN Explicit Null Label Support with BGP IPv4 Label Session

Configuring CSC-CE with BGP: Example

Verifying Explicit Null Configuration: Example

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Command Reference

Feature Information for MPLS VPN—Explicit Null Label Support with BGP IPv4 Label Session

Glossary


MPLS VPN—Explicit Null Label Support with BGP IPv4 Label Session

First Published: January 20, 2004
Last Updated: February 27, 2009

The MPLS VPN—Explicit Null Label Support with BGP IPv4 Label Session feature provides a method to advertise explicit null in a Border Gateway Protocol (BGP) label session for a carrier supporting carrier (CSC) customer edge (CE) router.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for MPLS VPN—Explicit Null Label Support with BGP IPv4 Label Session" section.

Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Contents

•Prerequisites for MPLS—VPN Explicit Null Label Support with BGP IPv4 Label Session

•Restrictions for MPLS—VPN Explicit Null Label Support with BGP IPv4 Label Session

•Information About MPLS—VPN Explicit Null Label Support with BGP IPv4 Label Session

•How to Configure MPLS—VPN Explicit Null Label Support with BGP IPv4 Label Session

•Configuration Examples for MPLS—VPN Explicit Null Label Support with BGP IPv4 Label Session

•Additional References

•Command Reference

•Feature Information for MPLS VPN—Explicit Null Label Support with BGP IPv4 Label Session

•Glossary

Prerequisites for MPLS—VPN Explicit Null Label Support with BGP IPv4 Label Session

•You must configure your network for Multiprotocol Label Switching (MPLS) Virtual Private Network (VPN).

•You must configure BGP to distribute labels between the CSC-CE and CSC-provider edge (PE) routers.

Restrictions for MPLS—VPN Explicit Null Label Support with BGP IPv4 Label Session

•Configure an explicit null label only in a CSC-CE topology.

•Configure an explicit null label only on a per-neighbor basis.

Information About MPLS—VPN Explicit Null Label Support with BGP IPv4 Label Session

To configure the MPLS—VPN Explicit Null Label Support BGP IPv4 Label Session feature, you need to understand the following concepts:

•Feature Design of the MPLS—VPN Explicit Null Label Support with BGP IPv4 Label Session Feature

•Benefits of the MPLS—VPN Explicit Null Label Support BGP IPv4 Label Session Feature

Feature Design of the MPLS—VPN Explicit Null Label Support with BGP IPv4 Label Session Feature

On a CSC-CE with BGP IPv4 label distribution, BGP advertises an implicit null label for directly connected routes. This causes the previous hop (penultimate) router to do penultimate hop popping (PHP).

The MPLS—VPN Explicit Null Label Support BGP IPv4 Label Session feature makes the penultimate router swap the incoming label for (or impose) the explicit null label. This action forces the egress router to process the explicit null label by popping it and inspecting the packet that remains.

Benefits of the MPLS—VPN Explicit Null Label Support BGP IPv4 Label Session Feature

The explicit null label helps to preserve quality of service (QoS) bits from one Service Level Agreement (SLA) to another until the packets reach their CSC-CE destination.

How to Configure MPLS—VPN Explicit Null Label Support with BGP IPv4 Label Session

This section contains the following procedures:

•Configuring CSC with BGP (required)

•Verifying Explicit Null Configuration (optional)

Configuring CSC with BGP

Perform this task to configure CSC with BGP.

SUMMARY STEPS

1. enable

2. configure terminal

3. router bgp autonomous system-number

4. address-family ipv4 [unicast]

5. neighbor ip-address send-label explicit-null

6. neighbor {ip-address | peer-group-name | ipv6-address} activate

7. exit

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

router bgp autonomous system-number

Example:

Router(config)# router bgp 100

Enters router configuration mode and configures the router to run a BGP process.

Step 4 

address-family ipv4 [unicast]

Example:

Router(config-router)# address-family ipv4

Enters address family configuration mode for the IPv4 address family from which you can configure routing sessions that use standard IPv4 address prefixes.

Step 5 

neighbor ip-address send-label explicit-null

Example:

Router(config-router-af)# neighbor 10.0.0.2 send-label explicit-null

Advertises the capability of a router to send MPLS labels with BGP routes.

•The explicit-null keyword allows a CSC-CE router to send labels with a value of 0 to its neighbor.

Step 6 

neighbor {ip-address | peer-group-name | ipv6-address} activate

Example:

Router(config-router-af)# neighbor 192.168.99.70 activate

Enables the neighbor to exchange prefixes for the IPv4 address family with the local router.

Step 7 

exit

Example:

Router(config-router-af)# exit

Exits address family configuration mode and returns the router to router configuration mode.

•Repeat this step to exit router configuration mode and return the router to global configuration mode.

Verifying Explicit Null Configuration

Perform this task to verify that the explicit null option is configured.

SUMMARY STEPS

1. enable

2. show ip bgp neighbors [ip-address [advertised-routes | dampened-routes | flap-statistics |
paths [regexp] | received prefix-filter | received-routes | routes]]

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2 

show ip bgp neighbors [ip-address [advertised-routes | dampened-routes | flap-statistics | paths [regexp] | received prefix-filter | received-routes | routes]]


Example:

Router# show ip bgp neighbors

Displays information about the TCP and BGP connections to neighbors including explicit null.

•The optional ip-address argument displays the IP address of the neighbor whose routes you have learned If you omit this argument, all neighbors are displayed.

•The optional advertised-routes keyword displays all the routes the router has advertised to the neighbor.

•The optional dampened-routes keyword displays the dampened routes to the neighbor at the IP address specified.

•The optional flap statistics keyword displays the flap statistics of the routes learned from the specified neighbor (external BGP [eBGP]peers only)

•The optional path regexp keyword-argument combination displays autonomous system paths learned from the specified neighbor. An optional regular expression can be used to filter the output.

•The optional received prefix-filter keyword displays the configured prefix list filter for the specified IP address.

•The optional received-routes keyword displays all received routes (both accepted and rejected) from the specified neighbor.

•The optional routes keyword displays all routes that are received and accepted. This is a subset of the output from the received-routes keyword.

Configuration Examples for MPLS—VPN Explicit Null Label Support with BGP IPv4 Label Session

This section provides the following configuration examples:

•Configuring CSC-CE with BGP: Example

•Verifying Explicit Null Configuration: Example

Configuring CSC-CE with BGP: Example

In the following CSC-CE example, CSC is configured with BGP to distribute labels and to advertise explicit null for all its connected routes: 

Router(config-router-af)# neighbor 10.0.0.0 send-label explicit-null


router bgp 100

 bgp log-neighbor-changes

 neighbor 10.0.0.0 remote-as 200

 !

address-family ipv4

 neighbor 10.0.0.0 activate

 neighbor 10.0.0.0 send-label explicit-null

 no auto-summary

 no synchronization

 exit-address-family

Verifying Explicit Null Configuration: Example

This section provides sample output from the show ip bgp neighbors command.

In this example, the show ip bgp neighbors command displays information about connected BGP neighbors, including IP addresses, version numbers, neighbor capabilities, message statistics, and address family statistics that show if explicit null is configured: 

Router# show ip bgp neighbors 


BGP neighbor is 10.0.0.2,  remote AS 300, external link

  BGP version 4, remote router ID 10.0.0.20

  BGP state = Established, up for 00:45:16

  Last read 00:00:16, hold time is 180, keepalive interval is 60 seconds

  Neighbor capabilities:

    Route refresh: advertised and received(new)

    Address family IPv4 Unicast: advertised and received

    ipv4 MPLS Label capability: advertised and received

  Message statistics:

    InQ depth is 0

    OutQ depth is 0

                         Sent       Rcvd

    Opens:                  1          1

    Notifications:          0          0

    Updates:                1          2

    Keepalives:            47         47

    Route Refresh:          0          0

    Total:                 49         50

  Default minimum time between advertisement runs is 30 seconds


 For address family: IPv4 Unicast

  BGP table version 9, neighbor version 9/0

  Output queue sizes : 0 self, 0 replicated

  Index 1, Offset 0, Mask 0x2

  Member of update-group 1

  My AS number is allowed for 3 number of times

  AF-dependant capabilities:

    Outbound Route Filter (ORF) type (128) Prefix-list:

  Sending Prefix & Label(advertise explicit-null set)       !Explicit null is configured

                                 Sent       Rcvd

  Prefix activity:               ----       ----

    Prefixes Current:               3          3 (Consumes 144 bytes)

    Prefixes Total:                 3          6

    Implicit Withdraw:              0          3

    Explicit Withdraw:              0          0

    .........	

    .........

Additional References

The following sections provide references related to the MPLS—VPN Explicit Null Label with BGP IPv4 Label Session feature.

Related Documents


Standards

Standards
Title

No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.

—


MIBs

MIBs
MIBs Link

No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs


RFCs

RFCs
Title

RFC 1163

A Border Gateway Protocol

RFC 1164

Application of the Border Gateway Protocol in the Internet

RFC 2283

Multiprotocol Extensions for BGP-4

RFC 2547

BGP/MPLS VPNs

RFC 3107

Carrying Label Information in BGP-4


Technical Assistance

Description
Link

The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies.

To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.

Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

http://www.cisco.com/techsupport


Command Reference

The following commands are introduced or modified in the feature or features documented in this module. For information about these commands, see the Cisco IOS Multiprotocol Label Switching Command Reference at http://www.cisco.com/en/US/docs/ios/mpls/command/reference/
mp_book.html. For information about all Cisco IOS commands, use the Command Lookup Tool at http://tools.cisco.com/Support/CLILookup or the Cisco IOS Master Command List, All Releases, at http://www.cisco.com/en/US/docs/ios/mcl/allreleasemcl/all_book.html.

•debug ip bgp

•neighbor send-label explicit-null

•show ip bgp neighbors

•show ip bgp vpnv4

•show mpls forwarding-table

Feature Information for MPLS VPN—Explicit Null Label Support with BGP IPv4 Label Session

Table 1 lists the release history for this feature.

Not all commands may be available in your Cisco IOS software release. For release information about a specific command, see the command reference documentation.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS and Catalyst OS software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Note Table 1 lists only the Cisco IOS software release that introduced support for a given feature in a given Cisco IOS software release train. Unless noted otherwise, subsequent releases of that Cisco IOS software release train also support that feature.

Table 1 Feature Information for MPLS VPN—Explicit Null Label Support with BGP IPv4 Label Session

Feature Name
Releases
Feature Information

MPLS VPN—Explicit Null Label Support with BGP IPv4 Label Session

12.0(27)S
12.0(27)S1
12.2(28)SB
12.2(33)SRA
12.2(33)SXH

The MPLS VPN—Explicit Null Label Support with BGP IPv4 Label Session feature provides a method to advertise explicit null in a BGP label session for a carrier supporting carrier (CSC) customer edge (CE) router.

In 12.0(27)S, this feature was introduced.

In 12.0(27)S1, support was added for the Cisco 12000 series Internet routers.

In 12.2(28)SB, support was added for the Cisco 10000 series router.

This feature was integrated into Cisco IOS Release 12.2(33)SRA.

This feature was integrated into Cisco IOS Release 12.2(33)SXH.

The following commands were introduced or modified: debug ip bgp, neighbor send-label explicit-null, show ip bgp neighbors, show ip bgp vpnv4, show mpls forwarding-table.


Glossary

BGP—Border Gateway Protocol. The exterior Border Gateway Protocol used to exchange routing information between routers in separate autonomous systems. BGP uses TCP. Because TCP is a reliable protocol, BGP does not experience problems with dropped or fragmented data packets.

CE router—customer edge router. A router on the border between a VPN provider and a VPN customer that belongs to the customer.

eBGP—external Border Gateway Protocol. A BGP session between routers in different autonomous systems. When a pair of routers in different autonomous systems are more than one IP hop away from each other, an external BGP session between those two routers is called multihop external BGP.

label—A short, fixed-length data identifier that tells switching nodes how to forward data (packets or cells).

label distribution—The techniques and processes used to cause routed traffic to travel through the network on a path other than the one that would have been chosen if standard routing methods had been used.

LDP—Label Distribution Protocol. The protocol that supports MPLS hop-by-hop forwarding by distributing bindings between labels and network prefixes. The Cisco proprietary version of this protocol is the Tag Distribution Protocol (TDP).

LSP—label switched path. A configured connection between two routers, in which MPLS is used to carry packets. A path created by the concatenation of one or more label switched hops, allowing a packet to be forwarded by swapping labels from an MPLS node to another MPLS node.

MPLS—Multiprotocol Label Switching. A method for directing packets primarily through Layer 2 switching rather than Layer 3 routing. In MPLS, packets are assigned short, fixed-length labels at the ingress to an MPLS cloud by using the concept of forwarding equivalence classes. Within the MPLS domain, the labels are used to make forwarding decisions mostly without recourse to the original packet headers; formerly known as tag switching.

NLRI—Network Layer Reachability Information. BGP sends routing update messages containing NLRI, which describes the route. In this context, an NLRI is a prefix. A BGP update message carries one or more NLRI prefixes and the attributes of a route for the NLRI prefixes. The route attributes include a BGP next hop gateway address, community values, and other information.

PE router—provider edge router. A router on the border between a VPN provider and a VPN customer that belongs to the provider.

QoS—quality of service. A measure of performance for a transmission system that reflects its transmission quality and service availability.

router—A network layer device that uses one or more metrics to determine the optimal path along which network traffic should be forwarded. Routers forward packets from one network to another based on network layer information.

VPN—Virtual Private Network. A secure IP-based network that shares resources on one or more physical networks. A VPN contains geographically dispersed sites that can communicate securely over a shared backbone.

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