BGP Community filtering

[pankaj_cisco111]

Pls Could you explain the following BGP Community tags scenario ?

3 Routers r1, r2 & r3 are in Different BGP AS.

R1 --- AS 1

R2 --- AS 2

R3 --- AS 3

R1 establishes EBGP with R2 & R3

NOW The below networks are advertised under BGP on R2 & R3

R2 : 114.10.10.2/24, 114.20.20.2/24

R3 : 115.10.10.3/24, 115.20.20.3/24

NOW Ensure that R1 uses AS 2 to connect to 114.10.10.0/24 & 115.10.10.0/24 & AS 3 to 114.20.20.0/24 & 115.20.20.0/24. WE must use use community tags in AS 2 & 3 and neighbor command on R1 to accomplish this task.

Waiting ur explanations

[aghaznavi]

Community tags in bgp are used for controlling the distribution of routing information.The available ones are .Refer the following url given below for more details,

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr_c/ipcprt2/1cfbgp.htm#wp1001855

[balajitvk]

Hi,

U can do this very well provided AS2 and AS3 should attach the community on their outgoing routes and AS1 should interpret that community value and have to set local-preference accordingly.

For example, When R3 advertise 114.10.10.0 it should set the community value and when R2 advertise 114.20.20.0 /24, it should set the community value towards R1

And R1 should match that community value and should set lesser local-preference to that so it forward packets in the other route.

Rgs,