modified gate

Question

Consider a network with five nodes, N1 to N5, as shown as below.

The network uses a Distance Vector Routing protocol. Once the routes have been stabilized, the distance vectors at different nodes are as following.

N1: (0, 1, 7, 8, 4)

N2: (1, 0, 6, 7, 3)

N3: (7, 6, 0, 2, 6)

N4: (8, 7, 2, 0, 4)

N5: (4, 3, 6, 4, 0)

Each distance vector is the distance of the best known path at that instance to nodes, N1 to N5, where the distance to itself is 0. Also all links are symmetric and the cost is identical in both directions. In each round, all nodes exchange their distance vectors with their respective neighbors. Then all nodes update their distance vectors. In between two rounds, any change in cost of a link will cause the two incident nodes to change only that entry in their distance vectors.

The cost of link N2-N3 reduces to 2 (in both directions). After the next round of updates, the link N1-N2 goes down. N2 will reflect this change immediately in its distance vector as cost, ∞∞. After the NEXT ROUND of update, what will be the cost to N1 in the distance vector of N4?

I think the answer should be 5. Am I right?

Answer 1

Yes. I'm also getting 5. I'm getting the following table for N4 after this round of update:

destination,cost, nextHop

N1, 5, N3

N2, 4, N3

N3, 2, N3

N4, 0, -

N5, 4, N5