BGP Multihoming

[p.holley]

I am running IBGP between RTA and RTB in AS 100. I am using the bgp network command to advertise network a.b.c.d into bgp on both routers.

RTA is an EBGP neighbor to ISP A in AS 200, and RTB is an EBGP neighbor to ISP B in AS 300.

How do I control the advertisement of network a.b.c.d from AS 100, so that RTA --> ISP A route is used, and if not available RTB ---> ISP is used.

Since both routers originate the a.b.c.d network, I am finding it hard to manipulate the outbound policy I so desire.

I tried to use local preference with RTA advertising a local preference of 200 to RTB for the network. But this will not work since RTB also originate the network a.b.c.d

If I decide to use the network command on only RTA, and use BGP to advertise network a.b.c.d to RTB. If RTA fails, how will RTB advertise this route?

What is the best way to have network a.b.c.d take path RTA ---> ISP A, and if RTA is not available take the path RTB --- ISP B ? Thanks

[pkhatri]

One possible way is to use a route-map on RTB to set the weight to 0 and the local-pref to 90.

E.g

router bgp 100

network a.b.c.d route-map Map

route-map Map permit 10

set weight 0

set local-preference 90

This way, RTB will prefer the route through RTA but will fall back to its own route should RTA stop injecting it into BGP.

HTH,

Paresh.

[p.holley]

Thanks buddy, I tried it in the lab and it works. Will do it in customer site tonight.