Question

A network uses a routing protocol where each router periodically shares its entire routing table with its immediate neighbours. Over time, the network experiences issues like slow convergence and routing loops (count-to-infinity problem). Determine the routing algorithm, which is most likely being used in this network.

• A. Link State Routing
• B. Distance Vector Routing
• C. Flooding Algorithm
• D. Hierarchical Routing

Hint:

Remember the phrase: "Distance Vector routers tell their neighbors about the whole world, while Link State routers tell the whole world about their neighbors."

Answer 1

The Correct Option is B

Concept:
Routing protocols are algorithms used by routers to determine the best path for data packets across a network. The two primary classes of interior gateway protocols are Distance Vector and Link State. The behavior described in the question—periodic sharing of the full table with neighbors—is the hallmark of the Distance Vector approach.

Step 1: Mechanism of Distance Vector Routing.
In Distance Vector (DV) routing, such as the Routing Information Protocol (RIP), each router maintains a table containing the distance (cost) and the vector (next hop) to every known destination.
• Sharing: Routers do not have a global map of the network. Instead, they "gossip" with their direct neighbors, sending their entire routing table at regular intervals (e.g., every 30 seconds).
• Calculation: Routers update their own tables using the Bellman-Ford algorithm based on the information received from neighbors.

Step 2: Identifying the Flaws.
The question mentions two specific problems:
• Slow Convergence: Since information propagates one hop at a time, it takes a long time for a change (like a link failure) to be known by distant routers.
• Count-to-Infinity Problem: This occurs when a link fails, but routers continue to increment the distance to that destination based on outdated information from each other. This creates a routing loop where the "distance" keeps increasing toward infinity.

Step 3: Comparison with Link State.
In contrast, Link State routing (like OSPF) only shares information about its own local links with all routers in the network (via flooding). Every router builds a complete map (topology) of the network and uses Dijkstra's algorithm. This converges much faster and is generally immune to the count-to-infinity problem.