Users Guide

Usage
Information
To verify statistics of routes rejected, use the show ip bgp neighbors command. If routes are
rejected, the session is reset. In the event of a failure, the existing BGP sessions flap. For updates
received from EBGP peers, BGP ensures that the first AS of the first AS segment is always the AS of the
peer, otherwise the update drops and the counter increments. The no version of this command turns off
the default.
NOTE: To configure these settings for a non default VRF instance, you must first enter the
ROUTER-CONFIG-VRF sub mode using the following commands:
1. Enter the ROUTER BGP mode using the router bgp as-number command.
2. From the ROUTER BGP mode, enter the ROUTER BGP VRF mode using the vrf vrf-name
command.
Example
OS10(conf-router-bgp-1)# enforce-first-as
Supported
Releases
10.3.0E or later
fall-over
Enables or disables BGP session fast fall-over for BGP neighbors.
Syntax
fall-over
Parameters None
Default Disabled
Command Mode ROUTER-NEIGHBOR
Usage
Information
Configure the BGP fast fall-over on a per-neighbor or peer-group basis. When you enable this command
on a template, it simultaneously enables on all peers that inherit the peer group template. When you
enable fall-over, BGP tracks IP reachability to the peer remote address and the peer local address.
Whenever either address becomes unreachable — no active route exists in the routing table for peer
IPv6 destinations or local address — BGP brings down the session with the peer. The no version of this
command disables fall-over.
Example
OS10(conf-router-neighbor)# fall-over
Supported
Releases
10.3.0E or later
fast-external-fallover
Resets BGP sessions immediately when a link to a directly connected external peer fails.
Syntax
fast-external-fallover
Parameters None
Default Not configured
Command Mode ROUTER-BGP
Usage
Information
Fast external fall-over terminates the EBGP session immediately after the IP unreachability or link failure
is detected. This only applies after you manually reset all existing BGP sessions. For the configuration to
take effect, use the clear ip bgp command. The no version of this command disables fast external
fallover.
NOTE: To configure these settings for a non default VRF instance, you must first enter the
ROUTER-CONFIG-VRF sub mode using the following commands:
1. Enter the ROUTER BGP mode using the router bgp as-number command.
Layer 3 671