Which of the following routing protocols is considered a distance-vector protocol?
Correct Answer: C
Detailed Explanation: Routing protocols are broadly classified based on how they calculate the best path for data to travel from a source to a destination. One such classification is the distance-vector routing protocol, which bases its decision on the number of hops (or distance) to reach a destination network. Among the options provided, Routing Information Protocol (RIP) is the classic example of a distance-vector routing protocol. How Distance-Vector Routing Works: Distance-vector protocols operate by having each router periodically send its entire routing table to its immediate neighbors. Routers use this information to calculate the shortest path to a destination based on a metric, which, in the case of RIP, is the hop count. The maximum number of hops allowed in RIP is 15, making it suitable only for smaller or less complex networks. If a destination is more than 15 hops away, it is considered unreachable. Characteristics of RIP: Simplicity: RIP is one of the simplest routing protocols, which made it popular in early networking environments. Periodic Updates: Routers using RIP send out their entire routing table at regular intervals (every 30 seconds by default). This periodic update can lead to slower convergence and increased network overhead. Count-to-Infinity Problem: One of the limitations of distance-vector protocols like RIP is the count-to-infinity problem, where routing loops can occur, and incorrect routing information can persist for a period before being corrected. Limited Scalability: Due to its hop count limit and slower convergence, RIP is generally not used in large or modern enterprise networks, which prefer more efficient protocols. Comparison with Other Protocols: OSPF (Option A): OSPF is a link-state routing protocol. It builds a complete map of the network topology, which allows it to calculate the shortest path using the Dijkstra algorithm. EIGRP (Option B): Although EIGRP has characteristics that resemble both distance-vector and link-state protocols, it is classified as a hybrid routing protocol because it uses advanced metrics and faster convergence techniques. IS-IS (Option D): IS-IS is also a link-state routing protocol, similar to OSPF, and it uses a complete topology database to make routing decisions. Conclusion: Among the options, RIP is the prototypical distance-vector routing protocol (Option C). Its reliance on hop count as the metric for determining the best path, combined with periodic updates and inherent limitations in scalability, clearly distinguishes it from the link-state or hybrid protocols listed in the other options. Understanding RIP’s characteristics is important, especially as it provides a baseline for comparing more advanced routing protocols.
This CCNA practice question helps students prepare for Cisco networking certification exams by testing knowledge of network fundamentals, routing, switching, and network security concepts.