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RE: bgp multihomed to one isp [7:80237] posted 12/04/2003
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You need to worry about egress (outbound) and ingress (inbound)


EGRESS (OUTBOUND)

modify weight if one router / local pref if more than one router (in your
network).. let's say weight cuz one router was all you had in your diagram.

set the weight really high on the t-3 session, and don't set
a weight on the t-1 provider so it uses the default route
of 0

router bgp 1
neighbor 1.1.1.1 remote-as 1234
neighbor 1.1.1.1 description T-3 ISP
neighbor 1.1.1.1 weight 50000
neighbor 2.2.2.2 remote-as 9999
neighbor 2.2.2.2 description T-1 ISP


INGRESS (INBOUND)

prepend the as-path a few times on the T-1 provider only. this will
make it look like more AS hops to your as via the T-1 provider.
Make sure the T-1 ISP ALLOWS this. Some don't.

router bgp 1
neighbor 2.2.2.2 route-map prepend out

route-map prepend permit 10
set as-path prepend 1 1 1 1 1



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