From: Carlos Trujillo Jimenez (nergal888@hotmail.com)
Date: Mon Nov 19 2007 - 10:16:28 ART
A practial and real example could be when you are peering an ebgp connection
with another router, and as a result of an AS ID MIGRATION in your bgp AS
DOMAIN, you must update the configuration in your local router to the new
AS, but what? if the providers cant update the configuration peering to your
new AS?
Solution: You must configure your old AS NUMBER only for the ebgp peering
with that neighbor, until he updates his peering with the new AS.
Do you remember that an AS (router) discard routes that have its own AS in
the AS-PATH of a given route?
I will try to explain:
There are complex redundat topologies where, if you set the local as for a
given ebgp peering connection, and if there is another as (some hops away
from you) and that AS is the same AS as you configure in the LOCAL AS
command, THAT AS CANT REACH your neighbor routes because you have used his
AS prepending it in the AS PATH list of that networks, and when he recibes
that routes he discards them, because he looks that in the AS PATH list its
his own as prepended.
So to prevent this type of issues you mut NO-PREPEND the LOCAL AS when you
are configuring and ebgp peer.
>From: itsfortarget@gmail.com
>X-OriginalArrivalTime: 19 Nov 2007 13:00:25.0060 (UTC)
>FILETIME=[269CA240:01C82AAC]
>
>hello,
>
>What is the need of LOCAL-AS command with BGP neighbour Command and watht
>is the significant of LOCAL-AS No prepend
>
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