One criterion for being selected as the best BGP route?

• A. The next-hop IP is reachable via an IGP
• B. The route with the shortest AS path length
• C. The path with the highest local preference
• D. The route with the lowest MED

Answer: (A)

In BGP best-path selection, a key gating condition is whether the next-hop address of a candidate route is reachable. If the next-hop cannot be reached through the IGP (or a static route), that path is not considered further and will not be installed as the best route, regardless of how favorable its other attributes seem. This reachability check happens before applying the usual decision factors like local preference, AS path length, origin, and MED. Only after confirming that the next-hop is reachable does the router compare the viable paths using those attributes to pick the best one. So ensuring the next-hop is reachable is the prerequisite that makes a path eligible for comparison and eventual selection.