BGP Enhanced Route Refresh
The BGP Enhanced Route Refresh feature provides a way for Border Gateway Protocol (BGP) to find route inconsistencies, and in that unlikely event, to synchronize BGP peers without a hard reset. The feature is enabled by default; there are two optional timers.
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see 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 for BGP Enhanced Route Refresh.
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Information About BGP Enhanced Route Refresh
BGP Enhanced Route Refresh Functionality
During session establishment, BGP peers exchange with each other their capability to do the BGP Enhanced Route Refresh feature. The feature is enabled by default.
It is not expected that the peers will become inconsistent with each other. That might only happen in an extreme corner case, and if that happens, this feature helps to identify that and synchronize the peers without a hard reset.
If two peers are capable of Enhanced Route Refresh, each peer will generate a Route-Refresh Start-of-RIB (SOR) message before it advertises the Adj-RIB-Out, and will generate a Route-Refresh End-of-RIB (EOR) message after it advertises the Adj-RIB-Out. A BGP speaker receiving an EOR message from its peer removes the routes that were not re-advertised as part of Route Refresh response by the peer.
In the unlikely event the router has stale routes remaining after receiving the EOR message or after the EOR timer expires, that means the peers were not consistent with each other. This information can be used to check whether routes are consistent.
BGP Enhanced Route Refresh Timers
These timers need not be configured under normal circumstances.You could configure one or both timers if you observe there is continuous route flapping to the extent that a Route Refresh EOR cannot be generated.
The first timer applies to the router when it should be receiving the EOR message, but is not receiving one. The second timer applies to the router when it should be sending the EOR message.
- Stale path timer--If the bgp refresh stalepath-time command is configured and the router does not receive a Route-Refresh EOR message after an Adj-RIB-Out, the router removes the stale routes from the BGP table after the timer expires. The stale path timer is started when the router receives a Route-Refresh SOR message.
- Maximum EOR timer--If the bgp refresh max-eor-time command is configured and the router is unable to generate a Route-Refresh EOR message, a Route-Refresh EOR message is generated after the timer expires.
Both timers are configurable. By default, they are both disabled (set to 0 seconds).
Syslog Messages Generated by the BGP Enhanced Route Refresh
The following are examples of syslog messages that are generated when a peer deletes stale routes after receiving the Route-Refresh EOR message or after the stale path timer expires. The messages help you to know whether the routers were inconsistent.
Net 300:300:126.96.36.199/0 from bgp neighbor IPv4 MDT 10.0.101.1 is stale after refresh EOR (rate-limited) Net 300:300:188.8.131.52/0 from bgp neighbor IPv4 MDT 10.0.101.1 is stale after refresh stale-path timer expiry (rate-limited)
The following are examples of messages logged after a Route-Refresh EOR or after the stale path timer expires, which indicate the total number of stale paths that were from the neighbor.
3 stale-paths deleted from bgp neighbor IPv4 MDT 10.0.101.1 after refresh EOR 3 stale-paths deleted from bgp neighbor IPv4 MDT 10.0.101.1 after refresh stale-path timer expiry
How to Set Timers for BGP Enhanced Route Refresh
Set Timers for BGP Enhanced Route Refresh
The BGP Enhanced Route Refresh feature is enabled by default; the timers are disabled by default. Perform this task if you want to set the optional timers.
Configuration Examples for BGP Enhanced Route Refresh
Example: Setting Timers for BGP Enhanced Route Refresh
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Feature Information for BGP Enhanced Route Refresh
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 Enhanced Route Refresh|
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