Re: [nsp] BGP loop detection

From: Philip Smith (pfs@cisco.com)
Date: Mon Jun 17 2002 - 10:38:52 EDT


Hi Nick,

Each stub network simply points a default route to you. Or you do a
"default-originate" on the eBGP peering to both stub networks. They don't
need to see the other /19 in their routing table - a default route is
sufficient. Simple solution... :-)

Check out
www.cisco.com/public/cons/seminars/NANOG23/BGP-Multihoming-Techniques.pdf
for a configuration example which solves this problem.

philip

--

At 22:17 17/06/2002 +0800, Nick Kraal wrote: >We have a customer that has transit services from us. They have split their >network into two /19 and run BGP with us at two different locations. Each >/19 is actually for two seperate businesses; one a tier-2 ISP and the other >VoIP provider. Two physically sperate networks are also running the same ASN >and are to peer with each other via our network. There is no internal >interconnectivity between them or any IGP running. > >The problem lies in that to reach each other they need to 'transit' via our >network and according to BGP, one cannot announce back the client prefixes >learnt from the other network and vice versa as both of them are running the >same ASN. This is to prevent routing loops. > >In this case is there a method to overwrite this so that the first /19 >network will be able to reach the second /19 network via ours? > >Thanks in advance. > >-nick/



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