How does the next-hop behavior in IGPs compare with BGP?

• A. An IGP uses the source IP address of a routing update as the next-hop address; BGP uses the IP address to reach the next AS.
• B. An IGP uses the interface address as the next-hop; BGP's next hop is the next AS address.
• C. IGP uses the router's loopback as next-hop by default; BGP uses the neighbor address.
• D. In both IGP and BGP, the next-hop is always the same.

Answer: (A)

In IGPs, routes inside the same routing domain are learned from neighboring routers, and the next-hop for those routes is typically the IP address of the router that advertised the route. In other words, the next-hop is the source IP of the update on the directly connected link, so each hop forwards toward that neighbor’s address.

In BGP, reachability across AS boundaries is driven by a dedicated next-hop value carried with the route. For routes learned from a neighbor outside your own AS, the next-hop is the address of that next hop toward the destination (often the address on the BGP session). This next-hop information can be preserved or updated in different BGP scenarios, but the important point is that BGP uses a specific next-hop attribute to indicate how to reach the destination beyond the local AS.

So the correct statement captures the general distinction: IGPs rely on the source address of the routing update as the next-hop, while BGP uses the next-hop IP to indicate how to reach the next hop toward the destination across AS boundaries.