IP Routing: BGP Configuration Guide, Cisco IOS Release 15S
BGP-RT and VPN Distinguisher Attribute Rewrite Wildcard
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BGP-RT and VPN Distinguisher Attribute Rewrite Wildcard

BGP-RT and VPN Distinguisher Attribute Rewrite Wildcard

The BGP—RT and VPN Distinguisher Attribute Rewrite Wildcard feature introduces the ability to set a range of route target (RT) community attributes or VPN distinguisher community attributes when mapping them. A network administrator might want to map one or more RTs at an egress ASBR to different RTs at an ingress ASBR. The VPN Distinguisher Attribute feature allows an administrator to map RTs to a VPN distinguisher that is carried through an eBGP and then mapped to RTs at an ingress ASBR. The mapping is achieved by configuring a route map that sets an RT range or VPN distinguisher range of extended community attributes. Specifying a range rather than individual RTs saves time and simplifies the configuration. Furthermore, a VPN distinguisher range allows more than one VPN distinguisher attribute per route-map clause, thereby removing the restriction that applied prior to this feature.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and 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 table at the end of this module.

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

Restrictions for BGP-RT and VPN Distinguisher Attribute Rewrite Wildcard

  • A range (specified in the set extcommunity rt command or the set extcommunity vpn-distinguisher command) can include a maximum of 450 extended communities.
  • The VPN distinguisher range is not relayed to an iBGP peer.

Information About BGP—RT and VPN Distinguisher Attribute Rewrite Wildcard

Benefits of RT and VPN Distinguisher Attribute Mapping Range

A network administrator might want to rewrite (or map) one or more route targets (RTs) at an egress ASBR to different RTs at an ingress ASBR. One use case would be to keep the RTs at the egress ASBR private from the ingress ASBR.

The rewrite is achieved by using inbound route maps, matching prefixes to route-map clauses that match inbound RTs, and mapping those RTs to different RTs recognized by the neighbor AS. Such a rewrite configuration could be complex on inbound route maps, with potentially hundreds of RTs that would need to be specified individually (configuring set extcommunity rt value1 value2 value3 ...). If the RTs being attached to the prefixes are consecutive, the configuration can be simplified by specifying a range of RTs. Thus, the benefits of the RT mapping range are saving time and simplifying the configuration.

Likewise, the mapping of RTs to a VPN distinguisher attribute (and vice versa) can also be simplified by specifying a range of RTs or VPN distinguishers. The BGP—VPN Distinguisher Attribute feature allows a network administrator to keep source RTs private from an ASBR in a destination AS. An RT at an egress ASBR is mapped to a VPN distinguisher, the VPN distinguisher is carried through the eBGP, and then it is mapped to an RT at the ingress ASBR.

The RT and VPN Distinguisher Attribute Mapping Range feature introduces the ability to specify a range of either route targets (RTs) or VPN distinguishers when mapping them.

Another benefit applies to setting a VPN distinguisher. Prior to this feature, only one set extcommunity vpn-distinguisher value was allowed per route-map clause. With the introduction of the mapping range, a range of VPN distinguishers can be set on a route.

How to Map RTs to RTs Using a Range

Replacing an RT with a Range of RTs

Perform this task on an egress ASBR to replace a route target (RT) with an RT range. Remember to replace the range of RTs with an RT on the ingress ASBR; that task is described in the “Replacing a Range of RTs with an RT” section.

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    ip extcommunity-list expanded-list {permit | deny} rt value

    4.    exit

    5.    route-map map-tag {permit | deny} [sequence-number]

    6.    match extcommunity extended-community-list-name

    7.    set extcomm-list extcommunity-name delete

    8.    set extcommunity rt range start-value end-value

    9.    exit

    10.    route-map map-tag {permit | deny} [sequence-number]

    11.    exit

    12.    router bgp as-number

    13.    neighbor ip-address remote-as autonomous-system-number

    14.    address-family vpnv4

    15.    neighbor ip-address activate

    16.    neighbor ip-address route-map map-tag out

    17.    exit-address-family


DETAILED STEPS
     Command or ActionPurpose
    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 ip extcommunity-list expanded-list {permit | deny} rt value


    Example:
    Router(config)# ip extcommunity-list 22 permit rt 101:100  
     

    Configures an IP extended community list to configure Virtual Private Network (VPN) route filtering, such that routes with the specified RT are in the extended community list.

    • This example permits routes having RT 101:100 into the extended community list 22.
     
    Step 4 exit


    Example:
    Router(config-extcomm-list)# exit 
     

    Exits the configuration mode and enters the next higher configuration mode.

     
    Step 5 route-map map-tag {permit | deny} [sequence-number]


    Example:
    Router(config)# route-map rt-mapping permit 10  
     

    Configures a route map that permits or denies the routes allowed by the subsequent match command.

    • This example permits the routes allowed by the subsequent match command.
     
    Step 6 match extcommunity extended-community-list-name


    Example:
    Router(config-route-map)# match extcommunity 22  
     

    Matches on the specified community list.

    • For this example, routes that match the extended community list 22 (which was configured in Step 3) are subject to the subsequent set commands.
     
    Step 7 set extcomm-list extcommunity-name delete


    Example:
    Router(config-route-map)# set extcomm-list 22 delete  
     

    Deletes the RT from routes that are in the specified extended community list.

    • For this example, RTs are deleted from routes that are in extended community list 22.
     
    Step 8 set extcommunity rt range start-value end-value


    Example:
    Router(config-route-map)# set extcommunity rt range 500:1 500:9 
     

    For the routes that are permitted by the route map, sets the specified RT range of extended community attributes, inclusive.

    • For this example, routes that match extended community 22 have their RT extended community attribute values set to 500:1, 500:2, 500:3, 500:4, 500:5, 500:6, 500:7, 500:8, and 500:9.
     
    Step 9 exit


    Example:
    Router(config-route-map)# exit 
     

    Exits route-map configuration mode and enters global configuration mode.

     
    Step 10 route-map map-tag {permit | deny} [sequence-number]


    Example:
    Router(config)# route-map rt-mapping permit 20  
     

    (Optional) Configures a route map entry that permits routes.

    • This example configures a route map entry that permits other routes not subject to the RT-to-RT range mapping. If you do not perform this step, all other routes are subject to an implicit deny.
     
    Step 11 exit


    Example:
    Router(config-route-map)# exit 
     

    Exits route-map configuration mode and enters global configuration mode.

     
    Step 12 router bgp as-number


    Example:
    Router(config)# router bgp 3000
     

    Enters router configuration mode and creates a BGP routing process.

     
    Step 13 neighbor ip-address remote-as autonomous-system-number


    Example:
    Router(config-router)# neighbor 192.168.103.1 remote-as 3000
     

    Specifies that the neighbor belongs to the autonomous system.

     
    Step 14 address-family vpnv4


    Example:
    Router(config-router)# address-family vpnv4
     

    Enters address family configuration mode to configure BGP peers to accept address family-specific configurations.

     
    Step 15 neighbor ip-address activate


    Example:
    Router(config-router-af)# neighbor 192.168.103.1 activate
     

    Activates the specified neighbor.

     
    Step 16 neighbor ip-address route-map map-tag out


    Example:
    Router(config-router-af)# neighbor 192.168.103.1 route-map rt-mapping out
     

    Applies the specified outgoing route map to the specified neighbor.

     
    Step 17 exit-address-family


    Example:
    Router(config-router-af)# exit-address-family 
     

    Exits address family configuration mode and enters privileged EXEC mode.

     

    Replacing a Range of RTs with an RT

    Perform this task on an ingress ASBR to replace an RT range of attributes with an RT attribute. This task assumes you already configured the egress ASBR to replace the RT with an RT range; that task is described in the “Replacing an RT with a Range of RTs” section.

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    ip extcommunity-list expanded-list {permit | deny} rt reg-exp

      4.    exit

      5.    route-map map-tag {permit | deny} [sequence-number]

      6.    match extcommunity extended-community-list-name

      7.    set extcomm-list extcommunity-name delete

      8.    set extcommunity rt value additive

      9.    exit

      10.    route-map map-tag {permit | deny} [sequence-number]

      11.    exit

      12.    router bgp as-number

      13.    neighbor ip-address remote-as autonomous-system-number

      14.    address-family vpnv4

      15.    neighbor ip-address activate

      16.    neighbor ip-address route-map map-tag in

      17.    exit-address-family


    DETAILED STEPS
       Command or ActionPurpose
      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 ip extcommunity-list expanded-list {permit | deny} rt reg-exp


      Example:
      Router(config)# ip extcommunity-list 128 permit rt 500:[1-9]  
       

      Configures an IP extended community list to configure Virtual Private Network (VPN) route filtering, such that routes with the specified RT range are in the extended community list.

      • This example permits routes having RTs in the range 500:1 to 500:9 into the extended community list 128.
       
      Step 4 exit


      Example:
      Router(config-extcomm-list)# exit 
       

      Exits the configuration mode and enters the next higher configuration mode.

       
      Step 5 route-map map-tag {permit | deny} [sequence-number]


      Example:
      Router(config)# route-map rtmap2 permit 10  
       

      Configures a route map that permits or denies the routes allowed by the subsequent match command.

      • This example permits the routes allowed by the subsequent match command.
       
      Step 6 match extcommunity extended-community-list-name


      Example:
      Router(config-route-map)# match extcommunity 128  
       

      Matches on the specified community list.

      • In this example, routes that match the extended community list 128 (which was configured in Step 3) are subject to the subsequent set commands.
       
      Step 7 set extcomm-list extcommunity-name delete


      Example:
      Router(config-route-map)# set extcomm-list 128 delete  
       

      Deletes the RTs in the range from routes that are in the specified extended community list.

      • In this example, RTs in the range are deleted from routes that are in extended community list 128.
       
      Step 8 set extcommunity rt value additive


      Example:
      Router(config-route-map)# set extcommunity rt 400:1 additive  
       

      Sets the routes that are permitted by the route map with the specified RT.

      • In this example, routes that match extended community 128 have their RT set to 400:1. The additive keyword causes the RT to be added to the RT list without replacing any RTs.
       
      Step 9 exit


      Example:
      Router(config-route-map)# exit 
       

      Exits route-map configuration mode and enters global configuration mode.

       
      Step 10 route-map map-tag {permit | deny} [sequence-number]


      Example:
      Router(config)# route-map rtmap2 permit 20  
       

      (Optional) Configures a route map entry that permits routes.

      • This example configures a route map entry that permits other routes not subject to the RT-range-to-RT mapping. If you do not perform this step, all other routes are subject to an implicit deny.
       
      Step 11 exit


      Example:
      Router(config-route-map)# exit 
       

      Exits route-map configuration mode and enters global configuration mode.

       
      Step 12 router bgp as-number


      Example:
      Router(config)# router bgp 4000
       

      Enters router configuration mode and creates a BGP routing process.

       
      Step 13 neighbor ip-address remote-as autonomous-system-number


      Example:
      Router(config-router)# neighbor 192.168.0.50 remote-as 4000
       

      Specifies that the neighbor belongs to the autonomous system.

       
      Step 14 address-family vpnv4


      Example:
      Router(config-router-af)# address-family vpnv4
       

      Enters address family configuration mode to configure BGP peers to accept address-family-specific configurations.

       
      Step 15 neighbor ip-address activate


      Example:
      Router(config-router-af)# neighbor 192.168.0.50 activate
       

      Activates the specified neighbor.

       
      Step 16 neighbor ip-address route-map map-tag in


      Example:
      Router(config-router-af)# neighbor 192.168.0.50 route-map rtmap2 in
       

      Applies the specified incoming route map to the specified neighbor.

       
      Step 17 exit-address-family


      Example:
      Router(config-router-af)# exit-address-family 
       

      Exits address family configuration mode and enters privileged EXEC mode.

       

      Configuration Examples for BGP—RT and VPN Distinguisher Attribute Rewrite Wildcard

      Example: Replacing an RT with a Range of RTs

      In the following example, on the egress ASBR, routes having RT 101:100 are in the extended community list 22. A route-map named rt-mapping matches on extended community list 22 and deletes the RT from routes in the community list. Routes that match the community list have their RT set to an RT in the range from 500:1 to 500:9. The route map is applied to the neighbor 192.168.103.1.

      Egress ASBR

      ip extcommunity-list 22 permit rt 101:100
      !
      route-map rt-mapping permit 10
       match extcommunity 22
       set extcomm-list 22 delete
       set extcommunity rt range 500:1 500:9
      !
      route-map rt-mapping permit 20
      !
      router bgp 3000
       neighbor 192.168.103.1 remote-as 3000
       address-family vpnv4
        neighbor 192.168.103.1 activate
        neighbor 192.168.103.1 route-map rt-mapping out
        exit-address-family
      !
            

      On the ingress ASBR, RTs in the range 500:1 to 500:9 belong to extended community list 128. A route map named rtmap2 maps those RTs to RT 400:1. The route map is applied to the neighbor 192.168.0.50.

      Ingress ASBR

      ip extcommunity-list 128 permit RT:500:[1-9]
      !
      route-map rtmap2 permit 10
       match extcommunity 128
       set extcomm-list 128 delete
       set extcommunity rt 400:1 additive
      !
      route-map rtmap2 permit 20
      !
      router bgp 4000
       neighbor 192.168.0.50 remote-as 4000
       address-family vpnv4
        neighbor 192.168.0.50 activate
        neighbor 192.168.0.50 route-map rtmap2 in
        exit-address-family
      !

      Example: Replacing an RT with a Range of VPN Distinguishers

      In the following example, on the egress ASBR, routes having RT 201:100 are in the extended community list 22. A route-map named rt-mapping matches on extended community list 22 and deletes the RT from routes in the community list. Routes that match the community list have their VPN distinguishers set to VPN distinguishers in the range from 600:1 to 600:8. The route map is applied to the neighbor 192.168.103.1.

      Egress ASBR

      ip extcommunity-list 22 permit rt 201:100
      !
      route-map rt-mapping permit 10
       match extcommunity 22
       set extcomm-list 22 delete
       set extcommunity vpn-distinguisher range 600:1 600:8
      !
      route-map rt-mapping permit 20
      !
      router bgp 3000
       neighbor 192.168.103.1 remote-as 3000
       address-family vpnv4
        neighbor 192.168.103.1 activate
        neighbor 192.168.103.1 route-map rt-mapping out
        exit-address-family
      !
            

      On the ingress ASBR, VPN distinguishers in the range 600:1 to 600:8 belong to extended community list 101. A route map named rtmap2 maps those VPN distinguishers to RT range 700:1 700:10. The route map is applied to the neighbor 192.168.0.50. The additive option adds the new range to the existing value without replacing it.

      Ingress ASBR

      ip extcommunity-list 101 permit VD:600:[1-8]
      !
      route-map rtmap2 permit 10
       match extcommunity 101
       set extcomm-list 101 delete
       set extcommunity rt 700:1 700:10 additive
      !
      route-map rtmap2 permit 20
      !
      router bgp 4000
       neighbor 192.168.0.50 remote-as 4000
       address-family vpnv4
        neighbor 192.168.0.50 activate
        neighbor 192.168.0.50 route-map rtmap2 in
        exit-address-family
      !

      Additional References for BGP-RT and VPN Distinguisher Attribute Rewrite Wildcard

      Related Documents

      Related Topic

      Document Title

      Cisco IOS commands

      Cisco IOS Master Commands List, All Releases

      BGP commands

      Cisco IOS IP Routing: BGP Command Reference

      BGP—VPN Distinguisher Attribute

      “BGP—VPN Distinguisher Attribute” module in the IP Routing: BGP Configuration Guide, Cisco IOS XE Release 3S

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      Feature Information for BGP—RT and VPN Distinguisher Attribute Rewrite Wildcard

      The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

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

      Table 1 Feature Information for BGP—RT and VPN Distinguisher Attribute Rewrite Wildcard

      Feature Name

      Releases

      Feature Information

      BGP—RT and VPN Distinguisher Attribute Rewrite Wildcard

      15.3(2)S

      Cisco IOS XE 3.9S

      The BGP—RT and VPN Distinguisher Attribute Rewrite Wildcard feature introduces the ability to set a range of route target (RT) community attributes or VPN distinguisher community attributes when mapping them. A network administrator might want to map one or more RTs at an egress ASBR to different RTs at an ingress ASBR. The VPN Distinguisher Attribute feature allows an administrator to map RTs to a VPN distinguisher that is carried through an eBGP and then mapped to RTs at an ingress ASBR. The mapping is achieved by configuring a route map that sets an RT range or VPN distinguisher range of extended community attributes. Specifying a range rather than individual RTs saves time and simplifies the configuration. Furthermore, a VPN distinguisher range allows more than one VPN distinguisher attribute per route-map clause, thereby removing the restriction that applied prior to this feature.

      The following commands were modified:

      • set extcommunity rt
      • set extcommunity vpn-distinguisher