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

[Ivan Pepelnjak]

If the "local-as" feature is what you're looking for, this might help you
get started: 

http://wiki.nil.com/Network_migration_or_merger_with_BGP_Local-AS_feature

Unfortunately I haven't covered the "replace-as" functionality yet, but
Arden has written a short article a while ago that covers it:

http://ardenpackeer.com/routing-protocols/bgp-allowas-in-bgp-local-as-tips-a
nd-tricks/

Best regards
Ivan
 
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http://blog.ioshints.info/

> -----Original Message-----
> From: Peter Rathlev [mailto:peter at rathlev.dk] 
> Sent: Thursday, May 07, 2009 9:08 AM
> To: Rocker Feller
> Cc: cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] Multiple BGP sessions on one router.
> 
> 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
> 
> 
> 
>