BGP Community to influence routing on client side

Unanswered Question
Jan 15th, 2010

Dear Guru's,

I dont know if this is possible, can i create a community that influence routing on client side based on what its received? Based on the drawing, the client is receiving the prefix on two AS's (AS300 and AS200) but i want the client to prefer AS200 using communities send by AS200 without using local preference on the client side (AS100).



I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 5 (1 ratings)
Edison Ortiz Fri, 01/15/2010 - 12:56

Communities can't influence traffic on itself. Communities are used to group prefixes under a common tag.

You can match on communities and then use the BGP Best Path attributes to influence traffic.

If you can't use LOCAL-PREF, you can use WEIGHT. Any reason why LOCAL-PREF is not acceptable?



jeffersoncbriones Fri, 01/15/2010 - 17:38

Hi Edison,

I just want to influence route on client without asking them to use local pref on their side to prefer the routes they receive. if i use weight, still they need to configure this on their side. I was thinking of using community to do this.



Marwan ALshawi Fri, 01/15/2010 - 18:51

Hi jeff

as Edison stated above the community cam be used in your case just like a route tag

it need to be combined with other BGP attributes to influence the path selection

if you have control on the other routers you may send summary from one router (AS) and more specific routes from the other router ( AS) in this case the more specific routes path will be preferred but this is only valid if you have control on the other routers

for example

client routr see from router1

and from router2   in this case all traffic going to and will use R2

if you dont have control on the other routers then you need to do some changes to the client router as described by edison above

good luck

if helpful Rate

Edison Ortiz Fri, 01/15/2010 - 19:15


You can use AS_PATH Prepend out of AS300 and the shortest AS path will be followed by traffic exiting AS100.




This Discussion