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Dell PowerEdge FN I/O Module Configuration Guide 9.10(0.0)

PDF

Configuring BGP Fast Fail-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 fail-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 you enable fail-over, 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 fail-over feature is configured on a per-neighbor or peer-group basis and is disabled by default.

To enable the BGP fast fail-over feature, use the following command.

To disable fast fail-over, use the [no] neighbor [neighbor | peer-group] fail-over command in CONFIGURATION ROUTER BGP mode.

Enable BGP Fast Fail-Over. CONFIG-ROUTER-BGP mode neighbor { ip-address | peer-group-name} fail-over

Example of Verifying that Fast Fail-Over is Enabled on a BGP Neighbor

To verify fast fail-over is enabled on a particular BGP neighbor, use the show ip bgp neighbors command. Because fast fail-over is disabled by default, it appears only if it has been enabled (shown in bold). 
Dell#sh ip bgp neighbors
                                 
                                 BGP neighbor is 100.100.100.100, remote AS 65517, internal link
                                 Member of peer-group test for session parameters
                                 BGP version 4, remote router ID 30.30.30.5
                                 BGP state ESTABLISHED, in this state for 00:19:15
                                 Last read 00:00:15, last write 00:00:06
                                 Hold time is 180, keepalive interval is 60 seconds
                                 Received 52 messages, 0 notifications, 0 in queue
                                 Sent 45 messages, 5 notifications, 0 in queue
                                 Received 6 updates, Sent 0 updates
                                 Route refresh request: received 0, sent 0
                                 Minimum time between advertisement runs is 5 seconds
                                 Minimum time before advertisements start is 0 seconds
                                 
                                 Capabilities received from neighbor for IPv4 Unicast :
                                 MULTIPROTO_EXT(1)
                                 ROUTE_REFRESH(2)
                                 CISCO_ROUTE_REFRESH(128)
                                 
                                 Capabilities advertised to neighbor for IPv4 Unicast :
                                 MULTIPROTO_EXT(1)
                                 ROUTE_REFRESH(2)
                                 CISCO_ROUTE_REFRESH(128)
                                 
                                 
                                 fail-over enabled
                                 
                                 Update source set to Loopback 0
                                 
                                 Peer active in peer-group outbound optimization
                                 
                                 For address family: IPv4 Unicast
                                 BGP table version 52, neighbor version 52
                                 4 accepted prefixes consume 16 bytes
                                 Prefix advertised 0, denied 0, withdrawn 0

To verify that fast fail-over is enabled on a peer-group, use the show ip bgp peer-group command (shown in bold). 

Dell#sh ip bgp peer-group
                                 
                                 Peer-group test
                                 
                                 fail-over enabled
                                 BGP version 4
                                 Minimum time between advertisement runs is 5 seconds
                                 
                                 For address family: IPv4 Unicast
                                 BGP neighbor is test
                                 Number of peers in this group 1
                                 Peer-group members (* - outbound optimized):
                                 100.100.100.100*
                                 
                                 Dell#
                                 
                                 router bgp 65517
                                 neighbor test peer-group
                                 neighbor test 
                                 fail-over
                                 neighbor test no shutdown

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