Which conditions are required for an iBGP neighbor relationship to form?

• A. Same AS number, defined neighbors and reachability
• B. Different AS numbers, random neighbors
• C. Direct physical connection only
• D. Only loopback addresses can be used

Answer: (A)

For an iBGP session to form, two routers must be in the same BGP system (same AS), each one must be explicitly configured to use the other as a neighbor, and they must be able to reach each other so a TCP session can be established. iBGP runs over TCP port 179, so a working IP path between the two devices is essential; this reachability can be through direct connections or through routing that makes the neighbor’s address reachable (loopbacks can be used with multihop, but that’s an implementation detail, not a requirement). The key distinction is that the AS numbers match and the neighbors are defined and reachable. If the AS numbers differ, that would be eBGP, not iBGP; random neighbors or a requirement for direct physical links aren’t part of the iBGP setup.