IP Routing: BGP Configuration Guide, Cisco IOS XE Release 3S (Cisco ASR 903)
BGP Graceful Shutdown
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BGP Graceful Shutdown

The BGP Graceful Shutdown feature reduces or eliminates the loss of traffic along a link being shut down for maintenance. Routers always have a valid route available during the convergence process. This feature is used primarily for maintenance on a link between a Provider Edge (PE), PE-PE, PE- Route Reflector (RR), PE-Customer Edge (CE) and CE.

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.

Information About BGP Graceful Shutdown

Purpose and Benefits of BGP Graceful Shutdown

There are times when planned maintenance operations cause routing changes in BGP. After the shutdown of eBGP and iBGP peering sessions between autonomous system border routers (ASBRs), BGP routers are temporarily unreachable during BGP convergence. The goal of gracefully shutting down one or more BGP sessions is to minimize traffic loss during the planned shutdown and subsequent reestablishment of the sessions.

The BGP Graceful Shutdown feature reduces or eliminates the loss of inbound or outbound traffic flows that were initially forwarded along the peering link that is being shut down for maintenance. This feature is primarily for PE-CE, PE-RR and PE-PE links. Lowering the local preference for paths received over the session being shutdown renders the affected paths less preferred by the BGP decision process, but still allows the paths to be used during the convergence while alternative paths are propagated to the affected routers. Therefore, routers always have a valid route available during the convergence process.

The feature also allows vendors to provide a graceful shutdown mechanism that does not require any router reconfiguration at maintenance time. The benefits of the BGP Graceful Shutdown feature are fewer lost packets and less time spent reconfiguring routers.

GSHUT Community

The GSHUT community is a well-known community used in conjunction with the BGP Graceful Shutdown feature. The GSHUT community attribute is applied to a neighbor specified by the neighbor shutdown graceful command, thereby gracefully shutting down the link in an expected number of seconds. The GSHUT community is always sent by the GSHUT initiator.

The GSHUT community is specified in a community list, which is referenced by a route map and then used to make policy routing decisions.

The GSHUT community can also be used in the show ip bgp community command to limit output to GSHUT routes.

How to Configure BGP Graceful Shutdown

Shutting Down a BGP Link Gracefully

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    router bgp autonomous-system-number

    4.    neighbor {ipv4-address | ipv6-address} remote-as number

    5.    neighbor {ipv4-address | ipv6-address | peer-group-name} shutdown graceful seconds {community value [local-preference value] | local-preference value}

    6.    end

    7.    show ip bgp community gshut


DETAILED STEPS
     Command or ActionPurpose
    Step 1 enable


    Example:
    Device> enable
     

    Enables privileged EXEC mode.

    • Enter your password if prompted.
     
    Step 2 configure terminal


    Example:
    Device# configure terminal
     

    Enters global configuration mode.

     
    Step 3 router bgp autonomous-system-number


    Example:
    Device(config)# router bgp 5000
     

    Configures a BGP routing process.

     
    Step 4 neighbor {ipv4-address | ipv6-address} remote-as number


    Example:
    Device(config-router)# neighbor 2001:db8:3::1 remote-as 5500
     

    Configures the autonomous system (AS) to which the neighbor belongs.

     
    Step 5 neighbor {ipv4-address | ipv6-address | peer-group-name} shutdown graceful seconds {community value [local-preference value] | local-preference value}


    Example:
    Device(config-router)# neighbor 2001:db8:3::1 shutdown graceful 600 community 1200 local-preference 300
     

    Configures the router to gracefully shut down the link to the specified peer in the specified number of seconds; advertises the route with the GSHUT (Graceful Shutdown) community; and advertises the route with another community or specifies a local preference value for the route, or both.

    • Make sure to specify an adequate amount of time for iBGP peers to converge and to choose an alternate path as the best path.
    • If the graceful keyword is used in the neighbor shutdown command, at least one of the two attributes (a community or local preference) must be configured. You may configure both attributes.
    • If the graceful keyword is used in the neighbor shutdown command, the route is advertised with the GSHUT community by default. You may also set one other community for policy routing purposes.
    • In this particular example, the route to the neighbor is configured to shut down in 600 seconds, is advertised with the GSHUT community and community 1200, and is configured with a local preference of 300.
    • The router receiving the advertisement looks at the community value(s) of the route and optionally uses the community value to apply routing policy. Filtering routes based on a community is done with the ip community-list command and a route map.
    • During the graceful shutdown, the neighbor shutdown command is not nvgened. After the timer expires, SHUTDOWN is nvgened.
     
    Step 6 end


    Example:
    Device(config-router)# end
     

    Returns to EXEC mode.

     
    Step 7show ip bgp community gshut


    Example:
    Device# show ip bgp community gshut
     

    (Optional) Displays information about the routes that are advertised with the well-known GSHUT community.

     

    Filtering BGP Routes Based on the GSHUT Community

    Perform this task on a BGP peer to the device where you enabled the BGP Graceful Shutdown feature.

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    router bgp autonomous-system-number

      4.    neighbor {ipv4-address | ipv6-address} remote-as number

      5.    neighbor {ipv4-address | ipv6-address} activate

      6.    neighbor {ipv4-address | ipv6-address} send-community

      7.    exit

      8.    route-map map-tag [permit | deny] [sequence-number]

      9.    match community {standard-list-number | expanded-list-number | community-list-name [exact]}

      10.    exit

      11.    ip community-list {standard | standard list-name} {deny | permit} gshut

      12.    router bgp autonomous-system-number

      13.    neighbor address route-map map-name in


    DETAILED STEPS
       Command or ActionPurpose
      Step 1 enable


      Example:
      Device> enable
       

      Enables privileged EXEC mode.

      • Enter your password if prompted.
       
      Step 2 configure terminal


      Example:
      Device# configure terminal
       

      Enters global configuration mode.

       
      Step 3 router bgp autonomous-system-number


      Example:
      Device(config)# router bgp 2000
       

      Configures a BGP routing process.

       
      Step 4 neighbor {ipv4-address | ipv6-address} remote-as number


      Example:
      Device(config-router)# neighbor 2001:db8:4::1 remote-as 1000
       

      Configures the autonomous system (AS) to which the neighbor belongs.

       
      Step 5 neighbor {ipv4-address | ipv6-address} activate


      Example:
      Device(config-router)# neighbor 2001:db8:4::1 activate
       

      Activates the neighbor.

       
      Step 6 neighbor {ipv4-address | ipv6-address} send-community


      Example:
      Device(config-router)# neighbor 2001:db8:4::1 send-community
       

      Enables BGP community exchange with the neighbor.

       
      Step 7 exit


      Example:
      Device(config-router)# exit
       

      Exits router configuration mode.

       
      Step 8 route-map map-tag [permit | deny] [sequence-number]


      Example:
      Device(config)# route-map RM_GSHUT deny 10
       

      Configures a route map to permit or deny routes for policy routing.

       
      Step 9 match community {standard-list-number | expanded-list-number | community-list-name [exact]}


      Example:
      Device(config-route-map)# match community GSHUT
       

      Configures that the routes that match ip community-list GSHUT will be policy routed.

       
      Step 10 exit


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

      Exits route-map configuration mode.

       
      Step 11 ip community-list {standard | standard list-name} {deny | permit} gshut


      Example:
      Device(config)# ip community-list standard GSHUT permit gshut
       

      Configures a community list and permits or denies routes that have the GSHUT community to the community list.

      • If you specify other communities in the same statement, there is a logical AND operation and all communities in the statement must match the communities for the route in order for the statement to be processed.
       
      Step 12 router bgp autonomous-system-number


      Example:
      Device(config)# router bgp 2000
       

      Configures a BGP routing process.

       
      Step 13neighbor address route-map map-name in


      Example:
      Device(config)# neighbor 2001:db8:4::1 route-map RM_GSHUT in
       

      Applies the route map to incoming routes from the specified neighbor.

      • In this example, the route map named RM_GSHUT denies routes from the specified neighbor that have the GSHUT community.
       

      Configuration Examples for BGP Graceful Shutdown

      Example: Shutting Down a BGP Link Gracefully

      Graceful Shutdown While Setting a Local-Preference

      This example gracefully shuts down the link to the specified neighbor in 600 seconds, adds the GSHUT community to the route, and sets a local preference of 500 for the route. 

      router bgp 1000
 neighbor 2001:db8:5::1 remote-as 2000
 neighbor 2001:db8:5::1 shutdown graceful 600 local-preference 500
 neighbor 2001:db8:5::1 send-community
 exit

      Graceful Shutdown While Setting an Additional Community

      This example gracefully shuts down the link to the specified neighbor in 600 seconds, and adds the GSHUT community and numbered community to the route. 

      router bgp 1000
 neighbor 2001:db8:5::1 remote-as 2000
 neighbor 2001:db8:5::1 shutdown graceful 600 community 1400
 neighbor 2001:db8:5::1 send-community
 exit

      Graceful Shutdown while Setting an Additional Community and Local-Preference

      This example gracefully shuts down the link to the specified neighbor in 600 seconds, adds the GSHUT community and the numbered community to the route, and sets a local preference of 500 to the route. 

      router bgp 1000
 neighbor 2001:db8:5::1 remote-as 2000
 neighbor 2001:db8:5::1 shutdown graceful 600 community 1400 local-preference 500
 neighbor 2001:db8:5::1 send-community
 exit

      Example: Filtering BGP Routes Based on the GSHUT Community

      In additional to being able to gracefully shut down a BGP route, another use of the GSHUT community is to configure a community list to filter routes with this community from getting into the BGP routing table.

      This example illustrates how to use a community list to filter incoming BGP routes based on the GSHUT community. In this example, a route map named RM_GSHUT denies routes based on a standard community list named GSHUT. The community list contains routes with the GSHUT community. The route map is then applied to incoming routes from the neighbor at 2001:db8:4::1. 

      router bgp 2000
 neighbor 2001:db8:4::1 remote-as 1000
 neighbor 2001:db8:4::1 activate
 neighbor 2001:db8:4::1 send-community
 exit
route-map RM_GSHUT deny 10
 match community GSHUT
 exit
ip community-list standard GSHUT permit gshut
router bgp 2000
 neighbor 2001:db8:4::1 route-map RM_GSHUT in

      Additional References

      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

      Standards and RFCs

      Standard/RFC

      Title

      RFC 6198

      Requirements for the Graceful Shutdown of BGP Sessions

      Technical Assistance

      Description

      Link

      The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

      http:/​/​www.cisco.com/​cisco/​web/​support/​index.html

      Feature Information for BGP Graceful Shutdown

      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 Graceful Shutdown

      Feature Name

      Releases

      Feature Information

      BGP Graceful Shutdown

      Cisco IOS XE Release 3.6S

      Cisco IOS XE Release 3.7S

      The BGP Graceful Shutdown feature reduces or eliminates the loss of traffic along a link being shut down for maintenance. Routers always have a valid route available during the convergence process.

      In Cisco IOS XE Release 3.7S, support was added for the Cisco ASR 903 router.

      The following commands were modified: ip community-list, neighbor shutdown, show ip bgp community, and show ip bgp vpnv4.

      BGP GSHUT Enhancement

      Cisco IOS XE Release 3.11S

      The BGP Graceful Shutdown (GSHUT) Enhancement feature enables graceful shutdown of either all neighbors or only virtual routing and forwarding (VRF) neighbors across BGP sessions.

      The following command was introduced: bgp graceful-shutdown all.