[c-nsp] Source address on BGP peering set up

[Mark Tinka]

On Friday 14 January 2005 15:14, Piltrafilla wrote:
> Hi people,

Hello.

>
> Anyone knows how BGP on a Cisco router choose source IP address for
> peering establishment if no "update-source" command is applied to
> neighbor? Is it only the primary IP address on the closest interface
> to neighbor?

Without manually specifying your source interface, BGP will find and use the 
Loopback interface with the highest IP address. Failing that, it will take 
the next highest IP address configured on the router (regardless of 
interface).

This can become a problem, especially if you keep adding/removing IP addresses 
on your router (customers, new routers, new segments, e.t.c.), hence the 
elegance of 'update-source'.

Mark.