Re: [nsp] BGP Multihoming -how to announce backup route???

From: Andrew Fort (afort@choqolat.org)
Date: Tue Nov 20 2001 - 01:34:07 EST


On Tue, Nov 20, 2001 at 11:05:06AM +0530, pankaj wrote:
>
> Now i want to receive traffic of two subnet A and B
> from ISP A, Subnet C, D from ISPB .
> If Isp A fails all traffic should come from B and if ISP B
> fails all traffic should come from ISPA.

announce all prefixes to both providers, with route-maps that prepend your AS to the "backup" provider for the prefixes you wish the provider to be backup for.

e.g. if you're AS100, your ISP-A is AS200, your ISP-B is AS300..

ip prefix-list ISP-A-backup permit 10.10.0.0/16
ip prefix-list ISP-B-backup permit 10.11.0.0/16

ip prefix-list announce permit 10.10.0.0/16
ip prefix-list announce permit 10.11.0.0/16

route-map ISP-A permit 10
 match ip address prefix-list ISP-A-backup
 set as-path prepend 100

route-map ISP-B permit 10
 match ip address prefix-list ISP-B-backup
 set as-path perpend 100

router bgp 100
 network 10.10.0.0 mask 255.255.0.0
 network 10.11.0.0 mask 255.255.0.0
 neighbor 1.2.3.4 remote-as 200
 neighbor 1.2.3.4 next-hop-self
 neighbor 1.2.3.4 prefix-list announce out
 neighbor 1.2.3.4 route-map ISP-A out
 no auto-summary

dont forget to have an IGP/IBGP route for each of the network/mask pairs you have listed in the bgp router, etc, etc.

for more, read:
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ics/icsbgp4.htm

and check out the stuff in:
http://www.cisco.com/public/cons/

-amf



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