Most Basic IBGP Rule

Most Basic IBGP Rule

IBGP routes learned from an ibgp peer, is not advertised to any other ibgp peer. Consider the picture below, good picture. JIf router C receives prefix from router A, it never advertises it to router B.

Of cource this is valid when all peers are configured as non-client environment, which is the default. But don’t forget if you are talking about a route reflector topology, rr advertises ibgp routes to it’s other clinets. “Clinet” keyword is so important here. I also would like to clarify the client and non-client confusion in route reflector topologies.

If prefix is received from a non-client, it’s advertised to only clients.

If prefix is received from a client, it’s advertised to both clients and non-clients.

To be more basic, the only “not advertised prefix” case is;

If prefix is received from non-client , it’s not advertised to non-client. All other is advertised J

                  +-------+        +-------+
                  |       |        |       |
                  | RTR-A |        | RTR-B |
                  |       |        |       |
                  +-------+        +-------+
                        \            /
                    IBGP \   ASX    / IBGP
                          \        /
                           +-------+
                           |       |
                           | RTR-C |
                           |       |
                           +-------+