Border Gateway Protocol | 207
BGP fast fall-over
By default, a BGP session is governed by the hold time. BGP routers typically carry large routing tables, so
frequent session resets are not desirable. The BGP fast fall-over feature reduces the convergence time
while maintaining stability. The connection to a BGP peer is immediately reset if a link to a directly
connected external peer fails.
When fall-over is enabled, BGP tracks IP reachability to the peer remote address and the peer local
address. Whenever either address becomes unreachable (for example, no active route exists in the routing
table for peer IPv6 destinations/local address), BGP brings down the session with the peer.
The BGP fast fall-over feature is configured on a per-neighbor or peer-group basis and is disabled by
default.
To disable Fast Fall-Over, use the
[no] neighbor [neighbor | peer-group] fall-over command in
CONFIGURATION ROUTER BGP mode
Use the
show ip bgp neighbors command as shown in Figure 9-22 to verify that fast fall-over is enabled
on a particular BGP neighbor. Note that since Fast Fall-Over is disabled by default, it will appear only if it
has been enabled.
Command Syntax Command Mode Purpose
neighbor {ip-address |
peer-group-name} fall-over
CONFIG-ROUTER-BGP Enable BGP Fast Fall-Over
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