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 |
| |
+-------+
