Provide an example of an iBGP configuration between two routers. Which option matches the example?

• A. R2 (config) # router bgp 65000; R2 (config-router)# neighbor 172.16.23.3 remote-as 65000; R3 (config) # router bgp 65000; R3 (config-router)# neighbor 172.16.23.2 remote-as 65000
• B. R2 (config) # router bgp 65000; R2 (config-router)# neighbor 172.16.23.3 remote-as 65100; R3 (config) # router bgp 65000; R3 (config-router)# neighbor 172.16.23.2 remote-as 65000
• C. R2 (config) # router bgp 65000; R2 (config-router)# neighbor 172.16.23.3 remote-as 65000; R3 (config) # router bgp 65001; R3 (config-router)# neighbor 172.16.23.2 remote-as 65000
• D. R3 (config) # router bgp 65000; R3 (config-router)# neighbor 172.16.23.3 remote-as 65000; R2 (config) # router bgp 65000; R2 (config-router)# neighbor 172.16.23.2 remote-as 65000

Answer: (A)

In iBGP, both peers must belong to the same autonomous system, and the session is formed by configuring the neighbor with the peer’s IP address on the directly connected link, while using the same AS number in the router bgp statement (remote-as equal to the local AS). This two-router setup is exactly what you’d expect: each router runs router bgp 65000 and points to the other router’s IP as the neighbor, with remote-as 65000 on both sides.

The best option shows R2 configuring a neighbor at 172.16.23.3 with remote-as 65000, and R3 configuring a neighbor at 172.16.23.2 with remote-as 65000. This matches an iBGP session between two routers in AS 65000 over the link between 172.16.23.2 and 172.16.23.3.

The other options fail because they mix in an eBGP scenario (remote-as different from 65000), or assign different AS numbers to the peers, or misconfigure the neighbor IPs (for example, pointing a router’s neighbor to its own address rather than the peer’s).