Refer to the exhibit. R2 is a route reflector, and R1 and R3 are route reflector clients. The route reflector learns the route to 172.16.25.0/24 from R1, but it does not advertise to R3. What is the reason the route is not advertised?
A.
R2 does not have a route to the next hop, so R2 does not advertise the prefix to other clients.
B.
Route reflector setup requires full IBGP mesh between the routers.
C.
In route reflector setup, only classful prefixes are advertised to other clients.
D.
In route reflector setups, prefixes are not advertised from one client to another.
There exists two issues and answer A only responds to the 1st one:
1. Even R2 learns the route (172.16.25.0/24) from R1, R2 BGP table shows the network without a “>” sign and the next-hop 209.165.200.255 same as R1 has, which is unreachable from R2 then the route is supposed to be unavailable in the routing table. To resolve this issue:
Configuring at R1 router bgp 65000 -> neighbor 192.168.2.2 next-hop-self
Then R2 will be able to reach the destination route 172.16.25.0/24
2. Even though R2 can reach the destination 172.16.25.0/24, which doesn’t advertise the route to its neighbor regarded as the BGP default advertisement rule so that R3 still can’t learn it. Thus need to set R2 as the route reflector:
Configuring at R2 router bgp 65000 -> neighbor 192.168.3.3 route-reflector-client
Given answer is correct, BGP needs the next-hop address to be reachable for a router to share that route with its peers. This basic rule helps avoid sending traffic to a dead end where the next hop can't be reached. R1 is sharing the 172.16.25.0/24 network with a next hop of 209.165.200.225. R2, acting as the route reflector, needs to have this next hop in its routing table to share this route with other clients or peers.
Will go for D, this is the closest answer, route reflector (R2) is receiving the route from R1, BGP between R2-R3 are established. I believe the command "neighbor 192.168.3.3 route-reflector-client " is missing on the R2 (not shown on the output), so R3 is not a client, only a BGP peer, so according to iBGP rules the R2 will not advertise the route that is received via IBG to non reflector clients
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