Re: BGP Convergence

I went through both options, And found following diff..

http://www.cisco.com/en/US/partner/docs/ios/iproute/command/reference/irp_bgp3.html#wp1013842
*neighbor** **ip-address** *fall-over [*bfd* | *route-map* *map-name*]
monitor the peering session of a specified neighbor for adjacency changes
and to deactivate the peering session,
Adjacency changes are detected, and terminated peering sessions are
deactivated in between the default or configured BGP scanning interval.

By default, the BGP scanner is used to poll the RIB for this information
every 60 seconds. During the 60 second time period between scan cycles,
Interior Gateway Protocol (IGP) instability or other network failures can
cause black holes and routing loops to temporarily form.

*bgp fast-external-fallover *
for BGP peering sessions with directly connected external peers
The session is immediately reset if link goes down. Only directly connected
peering sessions are supported.

http://www.cisco.com/en/US/partner/docs/ios/iproute/command/reference/irp_bgp2.html#wp1015842
*ip bgp fast-external-fallover* [*permit *| *deny*]
per-interface fast external fallover
overriding the global configuration

If we compare both the option,
In Terms of Faster Detection - Link Failures will be detected first and then
BGP Session failure
But - bgp fast-external-fallover - supports only directly connected
neighbors.

HTH
-Kaushal

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Received on Tue Jun 30 2009 - 10:59:02 ART