[c-nsp] Multiple BGP sessions on one router.

[Peter Rathlev]

On Thu, 2009-05-07 at 08:22 +0300, Rocker Feller wrote:
> I have been working with BGP for a few months now and am trying to get
> a grasp of it.
> 
> I have an assignment that requires to have multiple bgp sessions
> running on a single router and the prefixes advertised from each
> prefix appearing so.
> 
> Does this make sense? Am a bit foggy on this and would appreciate any
> direction advise on how this can be achieved.
> 
> What do I want to achieve?
> In short I want to consolidate to AS numbers in to one.

AFAIK you can't have two BGP instances on one Cisco device. You can do
something else though, namely use "local-as" on your neighbor session.
This would present your router as belonging to another AS.

+--------+          +--------+
| AS 100 |----------| AS 200 |
+--------+          +--------+

If you're on the left, paths from you would normally look like e.g. "100
i" to the ASBR in AS 200. If you configure "local-as 300" he would
instead see "300 100 i", as if you stuck the other AS in between you.
>From your side his paths would look like "300 200 i".

> Which options do I have to achieve this and with minimal disruptions
> to my customers?

Changing local-as requires the session to be reset to take effect.

Regards,
Peter