IP Routing: BGP Configuration Guide, Cisco IOS XE Release 3S (Cisco ASR 1000)
BGP Support for BFD
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BGP Support for BFD

Bidirectional Forwarding Detection (BFD) is a detection protocol designed to provide fast forwarding path failure detection times for all media types, encapsulations, topologies, and routing protocols. In addition to fast forwarding path failure detection, BFD provides a consistent failure detection method for network administrators. Because the network administrator can use BFD to detect forwarding path failures at a uniform rate, rather than the variable rates for different routing protocol hello mechanisms, network profiling and planning will be easier, and reconvergence time will be consistent and predictable. The main benefit of implementing BFD for BGP is a significantly faster reconvergence time.

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 Support for BFD

BFD for BGP

Bidirectional Forwarding Detection (BFD) is a detection protocol designed to provide fast forwarding path failure detection times for all media types, encapsulations, topologies, and routing protocols. In addition to fast forwarding path failure detection, BFD provides a consistent failure detection method for network administrators. Because the network administrator can use BFD to detect forwarding path failures at a uniform rate, rather than the variable rates for different routing protocol hello mechanisms, network profiling and planning will be easier, and reconvergence time will be consistent and predictable. The main benefit of implementing BFD for BGP is a marked decrease in reconvergence time.


Caution


BFD and BGP Graceful Restart capability cannot both be configured on a router running BGP. If an interface goes down, BFD detects the failure and indicates that the interface cannot be used for traffic forwarding and the BGP session goes down, but graceful restart still allows traffic forwarding on platforms that support NSF even though the BGP session is down, allowing traffic forwarding using the interface that is down. Configuring both BFD and BGP graceful restart for NSF on a router running BGP may result in suboptimal routing.


See also the “Configuring BGP Neighbor Session Options” chapter, the section “Configuring BFD for BGP IPv6 Neighbors.”

For more details about BFD, see the Cisco IOS IP Routing: BFD Configuration Guide.

How to Decrease BGP Convergence Time Using BFD

Prerequisites

  • Cisco Express Forwarding (CEF) and IP routing must be enabled on all participating routers.
  • BGP must be configured on the routers before BFD is deployed. You should implement fast convergence for the routing protocol that you are using. See the IP routing documentation for your version of Cisco IOS software for information on configuring fast convergence.

Restrictions

  • For the Cisco implementation of BFD Support for BGP in Cisco IOS Release15.1(1)SG, only asynchronous mode is supported. In asynchronous mode, either BFD peer can initiate a BFD session.
  • IPv6 encapsulation is supported.
  • BFD works only for directly-connected neighbors. BFD neighbors must be no more than one IP hop away. Multihop configurations are not supported.
  • Configuring both BFD and BGP Graceful Restart for NSF on a router running BGP may result in suboptimal routing.

Decreasing BGP Convergence Time Using BFD

You start a BFD process by configuring BFD on the interface. When the BFD process is started, no entries are created in the adjacency database, in other words, no BFD control packets are sent or received. The adjacency creation takes places once you have configured BFD support for the applicable routing protocols. The first two tasks must be configured to implement BFD support for BGP to reduce the BGP convergence time. The third task is an optional task to help monitor or troubleshoot BFD.

See also the “Configuring BFD for BGP IPv6 Neighbors” section in the “Configuring BGP Neighbor Session Options” module.

Configuring BFD Session Parameters on the Interface

The steps in this procedure show how to configure BFD on the interface by setting the baseline BFD session parameters on an interface. Repeat the steps in this procedure for each interface over which you want to run BFD sessions to BFD neighbors.

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    interface type number

    4.    bfd interval milliseconds min_rx milliseconds multiplier interval-multiplier

    5.    end


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 interface type number


    Example:
    Router(config)# interface FastEthernet 6/0
     

    Enters interface configuration mode.

     
    Step 4 bfd interval milliseconds min_rx milliseconds multiplier interval-multiplier


    Example:
    Router(config-if)# bfd interval 50 min_rx 50 multiplier 5
     

    Enables BFD on the interface.

     
    Step 5 end


    Example:
    Router(config-if)# end
     

    Exits interface configuration mode.

     

    Configuring BFD Support for BGP

    Perform this task to configure BFD support for BGP, so that BGP is a registered protocol with BFD and will receive forwarding path detection failure messages from BFD.

    Before You Begin
    • BGP must be running on all participating routers.
    • The baseline parameters for BFD sessions on the interfaces over which you want to run BFD sessions to BFD neighbors must be configured. See "Configuring BFD Session Parameters on the Interface" for more information.
    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    router bgp autonomous-system-number

      4.    neighbor ip-address fall-over bfd

      5.    end

      6.    show bfd neighbors [details]

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


    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 tag1
       

      Specifies a BGP process and enters router configuration mode.

       
      Step 4 neighbor ip-address fall-over bfd


      Example:
      Router(config-router)# neighbor 172.16.10.2 fall-over bfd
       

      Enables BFD support for fallover.

       
      Step 5 end


      Example:
      Router(config-router)# end
       

      Returns the router to privileged EXEC mode.

       
      Step 6 show bfd neighbors [details]


      Example:
      Router# show bfd neighbors detail
       

      Verifies that the BFD neighbor is active and displays the routing protocols that BFD has registered.

       
      Step 7 show ip bgp neighbors [ip-address [received-routes | routes | advertised-routes | paths [regexp] | dampened-routes | flap-statistics | received prefix-filter | policy [detail]]]


      Example:
      Router# show ip bgp neighbors
       

      Displays information about BGP and TCP connections to neighbors.

       

      Monitoring and Troubleshooting BFD

      To monitor or troubleshoot BFD, perform one or more of the steps in this section.

      SUMMARY STEPS

        1.    enable

        2.    show bfd neighbors [details]

        3.    debug bfd [event | packet | ipc-error | ipc-event | oir-error | oir-event]


      DETAILED STEPS
          Command or Action Purpose
        Step 1 enable


        Example:
        Router> enable
         

        Enables privileged EXEC mode.

        • Enter your password if prompted.
         
        Step 2 show bfd neighbors [details]


        Example:
        Router# show bfd neighbors details
         

        (Optional) Displays the BFD adjacency database.

        • The details keyword shows all BFD protocol parameters and timers per neighbor.
         
        Step 3 debug bfd [event | packet | ipc-error | ipc-event | oir-error | oir-event]


        Example:
        Router# debug bfd packet
         

        (Optional) Displays debugging information about BFD packets.

         

        Additional References

        Related Documents

        Related Topic

        Document Title

        Cisco IOS commands

        Cisco IOS Master Command List, All Releases

        BGP commands

        Cisco IOS IP Routing: BGP Command Reference

        BFD commands

        Cisco IOS IP Routing: Protocol Independent Command Reference

        Configuring BFD support for another routing protocol

        IP Routing: BFD Configuration Guide

        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 Support for BFD

        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 Support for BFD

        Feature Name

        Releases

        Feature Information

        BGP Support for BFD

        12.0(31)S

        12.4(4)T

        12.2(33)SRA

        12.2(33)SXH

        12.2(33)SB

        15.0(1)S

        15.1(1)SG

        15.2(1)E

        Cisco IOS XE Release 2.1

        Cisco IOS XE Release 3.5S

        Bidirectional Forwarding Detection (BFD) is a detection protocol designed to provide fast forwarding path failure detection times for all media types, encapsulations, topologies, and routing protocols. In addition to fast forwarding path failure detection, BFD provides a consistent failure detection method for network administrators. Because the network administrator can use BFD to detect forwarding path failures at a uniform rate, rather than the variable rates for different routing protocol hello mechanisms, network profiling and planning will be easier, and reconvergence time will be consistent and predictable. The main benefit of implementing BFD for BGP is a significantly faster reconvergence time.

        The following commands were introduced or modified by this feature: bfd, neighbor fall-over, show bfd neighbors, and show ip bgp neighbors.