bgp feed to customer

Richard Zheng rzheng at
Tue Jun 14 00:37:21 UTC 2011

> Hi Richard,
>        Could you run a bgp session on Router B ? I had to do this once for
> a customer because we had layer 3 switches on the edge with routing. I
> configured 2 BGP sessions at the customer's router. The first session was
> between  Customer C and Router B. I only sent the default route to the
> customer.  The next session was ebgp multihop between Router A and Customer
> C  with full routing.  I did allow the customer to announce the /30 to
> Router B just so Router A could learn the return path or you could just
> static route the /30 from Router A
> Now if the link Breaks between Router B and Customer C BGP will drop both
> sessions.
> Thanks
> Jim Gonzalez
When Router A redistributes external routes to OSPF, it sets the next hop to
itself. All the routers include Router B in the AS sends to traffic to
Router A which sends to Router B and causes a loop. The root cause is the
inability to set next-hop address for ospf route even though external routes
have a 'forward address' field.

It looks like that there are three solutions,
(a), Router B talks EBGP with Router C and then redistribute to OSPF
(b), Router B talks IBGP with Router A and then redistribute to OSPF,
redistribution may not be necessary if you don't care traffic from other
routers goes to Router A first, then to B and C.
(c), Create a tunnel between Routers A and C so that A sends traffic to
tunnel IP, instead router C

Personally I prefer (b) because only one EBGP is required to the customer. I
just need to figure out the IBGP config on Router A so that it only sends
the customer routes instead of the whole table.


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