Multiple choice

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

The net work uses a Distance Vector Routing protocol. Once the routes have 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 neighbours. 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.

After the update in the previous question, the link N1-N2 goes down. N2 will reflect this change immediately in its distance vector as cost,$\infty$. After the NEXT ROUND of update, what will be the cost to N1 in the distance vector of N3?

  1. 3

  2. 9

  3. 10
  4. $\infty$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

N3 has neighbors N2 and N4 N2 has made entry $\infty$ N4 has the distance of 8 to N1 N3 has the distance of 2 to N4 So, 2 + 8 = 10

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