What protocol replaced RIP as the main interior gateway protocol?

The correct answer is OSPF, which stands for Open Shortest Path First. OSPF replaced RIP (Routing Information Protocol) as the primary interior gateway protocol due to its ability to handle larger and more complex networks more efficiently.

OSPF utilizes a link-state routing algorithm, allowing routers to maintain a complete and up-to-date view of the network's topology. This improves the speed and accuracy of route calculations compared to RIP, which employs a distance-vector algorithm that can be slower to converge and is limited in terms of scalability. Furthermore, OSPF supports variable-length subnet masking (VLSM) and classless inter-domain routing (CIDR), enabling more efficient IP address utilization in larger networks.

While BGP (Border Gateway Protocol) is crucial for inter-domain routing between autonomous systems, it is not an interior gateway protocol and is therefore not applicable in this scenario. EIGRP (Enhanced Interior Gateway Routing Protocol) is indeed a notable protocol that has its strengths, but OSPF is widely recognized as the most prevalent and preferred replacement for RIP in many large enterprise networks. IS-IS (Intermediate System to Intermediate System) is another link-state protocol, but it is less commonly used compared to OSPF in modern networking practices.