BGP Community for ISP

Unanswered Question
Sep 4th, 2009

Hi Gurus,

Im on the process of designing a BGP network wherein my bgp clients can choose which upstream provider (which i have) they want their network to use, both for upstream and downstream. Is this possible using community ?


I have this problem too.
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Edison Ortiz Fri, 09/04/2009 - 04:42

For upstream, the process is simple - you would configure local-pref within your AS and the router with the highest local-pref will be used as the exit point.

For downstream, the process requires for you to contact the ISP. If you are using the same ISP (same BGP AS on the ISP) on all your connections, you can send a community to such ISP and they will match on such community for BGP attribute modification (local-pref). The ISP will need to provide the community to use on the BGP updates from your BGP routers.

You can also influence downstream flows without communities by using AS-PATH prepend. This BGP attribute is transitive so information will flow across BGP AS.



jeffersoncbriones Fri, 09/04/2009 - 18:44

Hi Edison,

Thanks for this info, im aware of using the locpref and prepend to influence route. Want we want to do is just give our bpg client (we are the isp connected to different upstream) info about what to community to use and their equivalent upstream. Like if i have upstreamA and UpstreamB, our client then can choose which upstream they want based on the community il be giving them.


Edison Ortiz Sat, 09/05/2009 - 07:50

Community is an arbitrary value on which the customer, you - as the ISP, and other ISPs must agree on.

You will match on those community values to perform modification on BGP attributes for traffic engineering. The community value on itself does not perform the traffic engineering that you are after.




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