BGP Consistency Checker
A BGP route inconsistency with a peer occurs when an update or a withdraw is not sent to a peer resulting in a null route. 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.
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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.
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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.
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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:
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“Net 10.0.0.0/32 has Nexthop-Label inconsistency.”
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“Net 10.0.0.0/32 in IPv4 Unicast has rib-out inconsistency for update-group 4 - outbound-policy fails.”
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