Specifying A Source Address For A Bgp Session - Juniper BGP - CONFIGURATION GUIDE V 11.1.X Configuration Manual

JUNOSe 11.1.x BGP and MPLS Configuration Guide

Specifying a Source Address for a BGP Session

By default, BGP uses the IP address of the outgoing interface toward the peer as the
source IP address for the TCP connection over which the BGP session runs. If the
outgoing interface goes down, the BGP session is dropped because the IP source
address is no longer valid. This is appropriate behavior for EBGP sessions because
the EBGP peers typically can reach each other only by virtue of being connected to
a common subnet.
For IBGP sessions, however, you typically want BGP sessions to be automatically
rerouted around interfaces that are down. You can issue the neighbor update-source
command to accomplish this. This command instructs BGP to use the IP address of
a specified interface as the source address of the underlying TCP connection. Typically,
a loopback interface is used because it is inherently stable.
For example, you can specify that BGP use loopback interface 2 as the source for
messages that it sends to peer 192.50.30.1:
neighbor update-source
The source address that you specify with the neighbor update-source command is
also used by BGP as the default value for the next hop address advertised for IPv4
or IPv6 prefixes.
The source addresses and next hop address that result from using the neighbor
update-source command vary depending on the configuration of the command.
Table 13 on page 31 lists the results for different configurations.
30
Configuring BGP Peer Groups
Use the no version to stop logging.
See bgp log-neighbor-changes
host1(config)#neighbor 192.50.30.1 update-source loopback 2
Use to allow a BGP session to use the IP address of a specific operational interface
as the source address for TCP connections.
If you specify a BGP peer group by using the peerGroupName argument, all the
members of the peer group inherit the characteristic configured with this
command unless it is overridden for a specific peer.
This command takes effect immediately and automatically bounces the BGP
session.
If you specify an interface in this command and the interface is later removed,
then this command is also removed from the router configuration.
Use the no version to restore the interface assignment to the closest interface.
See neighbor update-source