On Fri, 14 Jan 2005 15:45:30 +0200, Mark Tinka
<mti...@africaonline.co.sz> wrote:
On Friday 14 January 2005 15:14, Piltrafilla wrote:
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?
Debug is your friend if you can't find the info otherwise. It will
show you the source of the packet.
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 is not true, BGP will always "source" from the outgoing interface
unless you specify an interface with update-source. The source of the
packets is much different than the Router-ID which is what I think you
are confusing here. Router-ID is really only used as BGP best
route(path) selection in a tie-breaker scenario when everything else
is equal. The source address is used to establish peering(create the
TCP session)
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'.
19 messages in net.nether.puck.cisco-nsp[c-nsp] Source address on BGP peering...
