IP Routing: BFD Configuration Guide, Cisco IOS Release 15M&T
IS-IS Client for BFD C-Bit Support
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IS-IS Client for BFD C-Bit Support

The Bidirectional Forwarding Detection (BFD) protocol provides short-duration detection of failures in the path between adjacent forwarding engines while maintaining low networking overheads. The BFD IS-IS Client Support feature enables Intermediate System-to-Intermediate System (IS-IS) to use Bidirectional Forwarding Detection (BFD) support, which improves IS-IS convergence as BFD detection and failure times are faster than IS-IS convergence times in most network topologies. The IS-IS Client for BFD C-Bit Support feature enables the network to identify whether a BFD session failure is genuine or is the result of a control plane failure due to a router restart. When planning a router restart, you should configure this feature on all neighboring routers.

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.

Prerequisites for IS-IS Client for BFD C-Bit Support

  • IS-IS must be running on all participating devices.
  • The baseline parameters for BFD sessions must be configured on the interfaces that run BFD sessions to BFD neighbors.

Information About IS-IS Client for BFD C-Bit Support

IS-IS Restarts and BFD Sessions

The IS-IS Client for BFD C-Bit Support feature provides BFD with a way to signal to its peers whether the BFD implementation shares the same status as the control plane. When a neighboring router’s control plane restarts, a BFD session failure may occur, which does not actually represent a true forwarding failure. If this happens, you do not want the neighbors of the restarting router to react to the BFD session failure.

IS-IS does not have protocol extensions that allow it to signal in advance that it will be restarting. This means that the system cannot distinguish between a real forwarding failure and a restart. The IS-IS Client for BFD C-Bit Support feature allows you to configure the device to ignore control-plane related BFD session failures. We recommend that you configure this feature on the neighbors of a restarting device just prior to the planned restart of that device and that you remove the configuration after the restart has been completed.

The table below shows how the control plane independent failure status received from BFD on a session down event impacts IS-IS handling of that event.

Table 1 Control Plane Failure and Session Down Events

IS-IS Check Control Plane Failure

BFD Control Plane Independent Failure Status

IS-IS Action on BFD session 'DOWN' Event

Enabled

True

Accept session DOWN

Enabled

False

Ignore session DOWN

Disabled

True

Accept session DOWN

Disabled

False

Accept session DOWN

How to Configure IS-IS Client for BFD C-Bit Support

Configuring IS-IS Client for BFD C-Bit Support

Perfrom this task to enable control plane failure checking.

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    router isis

    4.    bfd check-control-plane-failure

    5.    end


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 isis


    Example:
    Device(config)# router isis
     

    Enables the IS-IS routing protocol and enters router configuration mode.

     
    Step 4 bfd check-control-plane-failure


    Example:
    Device(config-router)# bfd check-control-plane-failure
     

    Enables BFD control plane failure checking for the IS-IS routing protocol.

     
    Step 5 end


    Example:
    Device(config-router)# end
     

    Exits router configuration mode and returns to privileged EXEC mode.

     

    Configuration Examples for IS-IS Client for BFD C-Bit Support

    Example: Configuring IS-IS Client for BFD C-Bit Support

    The following example configures control plane failure detection on a router running the IS-IS protocol. 

    Device> enable
Device# configure terminal
Device(config)# router isis
Device(config-router)# bfd check-ctrl-plane-failure
Device(config-router)# end

    Additional References

    Related Documents

    Related Topic

    Document Title

    Cisco IOS commands

    Cisco IOS Master Command List, All Releases

    BFD commands: complete command syntax, command mode, command history, defaults, usage guidelines, and examples

    Cisco IOS IP Routing: Protocol-Independent Command Reference

    Configuring and monitoring IS-IS

    “Configuring Integrated IS-IS” module of the Cisco IOS IP Routing Protocols Configuration Guide

    Cisco IOS IPv6 features

    Cisco IOS IPv6 Feature Mapping

    Standards and RFCs

    Standard/RFC

    Title

    RFC 5882

    Generic Application of Bidirectional Forwarding Detection (BFD)

    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 IS-IS Client for BFD C-Bit Support

    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 2 Feature Information for IS-IS Client for BFD C-Bit Support

    Feature Name

    Releases

    Feature Information

    IS-IS Client for BFD C-Bit Support

    15.1(1)SY

    15.3(1)T

    The IS-IS Client for BFD C-Bit Support feature enables the network to identify whether a BFD session failure is genuine or is the result of a control plane failure due to a router restart.

    The following command was introduced: bfd check-ctrl-plane-failure.