Juniper JUNOSE 11.2.X BGP AND MPLS, Configuration Manual

Page: 67 / 742

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:
host1(config)# neighbor 192.50.30.1 update-source loopback 2
neighbor update-source
•
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
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.
Table 13: Source Addresses and Default Next Hop Addresses for Various Configurations
Default Next Hop
Value for IPv6
Prefixes Default Next Hop
Value for IPv4
Prefixes Source Address used
for TCPv4 and TCPv6
Connection
Configured Update
Source Address Configured Neighbor
Address
IPv4 source address
mapped to an IPv6
address IPv4 source address IPv4 source address IPv4 source address IPv4 neighbor address
Not allowed Not allowed Not allowed IPv6 source address IPv4 neighbor address
31 Copyright © 2010, Juniper Networks, Inc.
Chapter 1: Configuring BGP Routing