IP Routing: BGP Configuration Guide, Cisco IOS XE Release 3S (Cisco ASR 1000)
Configuring BGP Consistency Checker
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Configuring BGP Consistency Checker

The BGP Consistency Checker feature provides a way to identify certain types of BGP route inconsistencies with peers: next-hop label inconsistency, RIB-out inconsistency, and aggregation inconsistency. Upon finding such an inconsistency, the system sends a syslog error message and takes appropriate action if configured to do so.

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 Consistency Checker

BGP Consistency Checker

A BGP route inconsistency with a peer occurs when an update or a withdraw is not sent to a peer, and black-hole routing can result. To identify that issue, BGP consistency checker was created as a low-priority process that does nexthop-label, RIB-out, and aggregation consistency checks at a configurable interval. When enabled, BGP consistency checker is performed for all address families. Configuring BGP consistency checker is recommended.

Once the process identifies such an inconsistency, it will report the inconsistency with a syslog message and optionally take action if the auto-repair keyword is specified. The action taken depends on the type of inconsistency found.

  • Next-Hop Label Consistency Check—When two paths have the same next hop because they are advertised by the same provider edge router (PE), they should also have the same next-hop label. If the labels are different, there is an inconsistency. If the auto-repair keyword is specified, the system will send a route-refresh request.
  • RIB-Out Consistency Check—If a network passes an outbound policy and is not sent, or if a network does not pass an outbound policy and is sent, there is an inconsistency. If the auto-repair keyword is specified, the system will send a route-refresh request.
  • Aggregation Consistency Check—If specific routes and the aggregated route become out of sync, an inconsistency can occur. Either the error-message keyword or the auto-repair keyword will trigger aggregation reevaluation.

In the unlikely event that you receive a syslog message about an inconsistency, notify your Cisco technical support representative with the syslog message exactly as it appears. The following are examples of such syslog messages:

  • “Net 10.0.0.0/32 has Nexthop-Label inconsistency.”
  • “Net 10.0.0.0/32 in IPv4 Unicast has rib-out inconsistency for update-group 4 - outbound-policy fails.”

How to Configure BGP Consistency Checker

Configure BGP Consistency Checker

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    router bgp autonomous-system-number

    4.    bgp consistency-checker {error-message | auto-repair} [interval minutes]

    5.    end

    6.    show ip bgp [vpnv4 | vpnv6] all inconsistency nexthop-label


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 500
     

    Configures a BGP routing process.

     
    Step 4 bgp consistency-checker {error-message | auto-repair} [interval minutes]


    Example:
    Router(config-router)# bgp consistency-checker auto-repair interval 720
     

    Enables BGP consistency checker.

    • The default interval is 1440 minutes (one day). The range is 5 to 1440 minutes.
     
    Step 5 end


    Example:
    Router(config-router)# end
     

    Ends the current configuration and returns to privileged EXEC mode.

     
    Step 6 show ip bgp [vpnv4 | vpnv6] all inconsistency nexthop-label


    Example:
    Router# show ip bgp all inconsistency nexthop-label
     

    (Optional) Displays routes that have a nexthop-label inconsistency found.

    • This step is not part of configuring the feature; it is provided in case you receive a syslog message about a nexthop-label inconsistency and you want to display those routes.
     

    Configuration Examples for BGP Consistency Checker

    Example: Configuring BGP Consistency Checker

    The following example configures BGP consistency checker with auto-repair at the default interval of one day:

    router bgp 65000
     bgp consistency-checker auto-repair

    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

    Enabling BGP MIB support

    “BGP MIB Support” module in the IP Routing: BGP Configuration Guide

    Configuring SNMP Support

    SNMP Configuration Guide in the Cisco IOS Network Management Configuration Guide Library

    SNMP Commands

    Cisco IOS SNMP Support Command Reference

    Standards

    Standard

    Title

    None

    MIBs

    MIB

    MIBs Link

    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

    RFC

    Title

    RFC 1657

    BGP-4 MIB

    RFC 1771

    A Border Gateway Protocol 4 (BGP-4)

    RFC 2547

    BGP/MPLS VPNs

    RFC 2858

    Multiprotocol Extensions for BGP-4

    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 Consistency Checker

    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 Consistency Checker

    Feature Name

    Releases

    Feature Information

    BGP Consistency Checker

    Cisco IOS XE Release 3.3S

    Cisco IOS XE Release 3.4SG

    The BGP Consistency Checker feature provides a way to identify three types of BGP route inconsistencies with peers: next-hop label inconsistency, RIB-out inconsistency, and aggregation inconsistency. Upon finding such inconsistency, the system sends a syslog error message and takes appropriate action if configured to do so.

    The following command was introduced: bgp consistency-checker

    The following command was modified: show ip bgp vpnv4.