Hi ALL,
I have a question about bgp advertising prefixes back to the peer which advertised the route.
I am using IOS version 15.2.
My topology is very simple like this:
R3---------------R1--------------R2
R1 belongs to AS 1,R2 and R3 belongs to AS23.
R2 advertise 10.2.1.0/24 to R1 and R3 advertise 10.3.1.0/24 to R1
but when I "show ip bgp nei 1.1.12.2(R2's interface connected to R1) advertised-route , I saw the shown below:
R1#show ip bgp nei 1.1.12.2 advertised-routes
BGP table version is 5, local router ID is 1.1.13.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
Network Next Hop Metric LocPrf Weight Path
*> 10.2.1.0/24 1.1.12.2 0 0 23 i
*> 10.3.1.0/24 1.1.13.3 0 0 23 i
Total number of prefixes 2
that R1 advertise 10.2.1.0/24 back to R2.
when I shutdown the bgp session between R1 and R3, then R1 didn't advertise this route to R2 anymore.
I don't know why, Can someone help me explain it?
Thanks very much!