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Multihoming BGP advertisement

Level 1
Level 1



I have an ASR1001-X with 2 BGP peers and I have 2 /24 networks and want to advertise 1 networks by each upstream.



ip as-path access-list 10 permit ^$

ip as-path access-list 100 permit ^$
ip as-path access-list 200 permit ^$

router bgp 254
bgp router-id
bgp log-neighbor-changes

neighbor remote-as 100
neighbor remote-as 200

address-family ipv4
network mask
network mask

aggregate-address summary-only
aggregate-address summary-only

neighbor activate
neighbor route-map as100-in in
neighbor route-map as100-out out

neighbor activate
neighbor route-map as200-in in
neighbor route-map as200-out out


route-map as100-in permit 10
match as-path 10

route-map as100-out permit 10
match as-path 100

route-map as200-in permit 10
match as-path 10

route-map as200-out permit 10
match as-path 200

This is my config and what I want to do is to limit the next


advertise via AS100 and via as200. Idk if is possible with route maps or what, actually I'm trying to do it with prefix-lists.


Anyone in the same situation or can help with this?







1 Reply 1

Richard Burts
Hall of Fame
Hall of Fame

I have several comments and suggestions.

- you have configured your 2 BGP peers with different AS numbers so we are dealing with EBGP.

- you are applying an AS path list inbound to control what advertisement from your EBGP peers you will accept. That path list permits only ^$ and no advertisement from those peers will meet that condition. So you will accept no advertisement from those peers.

- you are applying an AS path list outbound to control what you will advertise to those peers. That path list permits only ^$ and that is the effective way to prevent your AS becoming a transit AS between those EBGP neighbors. So this is a good thing in your config.

- you want to advertise only a single network to one EBGP peer and a different network to the other EBGP peer. Your comment is that you are trying prefix lists for this but there are no prefix lists in what you posted. Prefix lists that permit only and permit only applied to outbound advertisements would be an effective way to accomplish your objective.






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