From: James (james@towardex.com)
Date: Sat Jul 24 2004 - 14:59:38 GMT-3
> I'll lab this up later, but my initial thought is that for this work, you
> would need the nei x.x.x.x update-source command.
As long as update-source on local router, and neighbor a.b.c.d on remote router
match to same IP, it won't slow down in bringing the session up.
> > > Is there any way i can overcome the specfic route reqired for
> > > BGP peering . Meaning when i am forming neighbor relationship with a
> > > peer , unless i have a specfic route for that peer in my route-table the
> > > peer relation ship is not comming ( i have default route ) . Its not
> > > taking the default route for forming peer relationship.
BGP is a TCP session, nothing more and nothing less. It uses FSM to help with
collision detection during session establishment routine, since in BGP, there
is no client-server relationship. Either peer can act as server/client at the
same time where whomever establishes TCP session first is the winner. With
that being said, if you have a default route and your router can get to remote
neighbor, and the remote neighbor can get back to you, you are all set on your
way to establish a TCP session.
The problem you may be seeing is that the remote neighbor you are peering with is
not directly connected to you. BGP by default, in what we call "single hop" peering
session will set the outgoing IP TTL to 1 (or 0 on some vendors). Meaning, as soon
as packet leaves the directly connected network, it dies due to ttl expiration.
In order to overcome such an issue, you do 'neighbor a.b.c.d ebgp-multihop $hopcount'
on both peers, where $hopcount equals to number of hops (or amount of TTL set)
between the peers. Usually people do either 2 for peering with a router thats next
to each other but not directly connected subnet, or 255 for simplicity sake.
-J
-- James Jun TowardEX Technologies, Inc. Technical Lead Network Design, Consulting, IT Outsourcing james@towardex.com Boston-based Colocation & Bandwidth Services cell: 1(978)-394-2867 web: http://www.towardex.com , noc: www.twdx.net
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