Documentation
Name
bgp router peer update-source - changes the source address of the BGP session
Synopsis
update-source <iface-address>
Arguments
- iface-address
Description
This command configures the address used as source to establish a BGP session with a neighbor router. The default source address depends on the outgoing interface selected when messages are sent towards the neighbor. This means that if the routing changes, the BGP session's source address might also change and the BGP session might break.
If the way the BGP session is routed may change or if the BGP session must be established between specific interfaces, the update-source command must be used to statically define the source address.
The following example illustrates how the command can be used in a scenario with a single BGP session between the loopback interfaces of two routers connected with two parallel links. In such a scenario, the default source address used on the side of router 1.0.0.1 would be 192.168.0.1 as this is the address of the outgoing address to reach node 1.0.0.2. Hence, the BGP session will not establish as the neighbor, router 1.0.0.2, expects an OPEN message with source address 1.0.0.1 and it will receive it with source address 192.168.0.1. To obtain the correct behavior, the source addresses used for the BGP session on both sides must be explicitly set to the addresses of the respective loopback interfaces using the update-source command.
net add node 1.0.0.1
net add node 1.0.0.2
net add link-ptp 1.0.0.1 192.168.0.1/30 1.0.0.2 192.168.0.2/30
net add link-ptp 1.0.0.1 192.168.0.5/30 1.0.0.2 192.168.0.6/30
# configure intradomain routing here (not shown)
bgp add router 1 1.0.0.1
bgp router 1.0.0.1
add peer 1 1.0.0.2
peer 1.0.0.2 update-source 1.0.0.1
peer 1.0.0.2 up
exit
bgp add router 1 1.0.0.2
bgp router 1.0.0.2
add peer 1 1.0.0.1
peer 1.0.0.1 update-source 1.0.0.2
peer 1.0.0.1 up
exit