GATE | Gate IT 2008 | Question 65

Two popular routing algorithms are Distance Vector(DV) and Link State (LS) routing. Which of the following are true?
(S1) Count to infinity is a problem only with DV and not LS routing
(S2) In LS, the shortest path algorithm is run only at one node
(S3) In DV, the shortest path algorithm is run only at one node
(S4) DV requires lesser number of network messages than LS

(A) S1, S2 and S4 only
(B) S1, S3 and S4 only
(C) S2 and S3 only
(D) S1 and S4 only


Answer: (D)

Explanation: S_1 is true since the Count to Infinity problem is associated with only Distance Vector algorithms and it does not affect Link State Algorithms.
S_2 is false since in Link State Algorithms the shortest route algorithm is run at every node after each node has broadcasted its neighbouring information to all other nodes.
S_3 is false since in Distance Vector Algorithms the shortest route algorithm is run at every node asynchronously whenever it receives a Distance Vector from its neighbours or whenever a link cost changes.
S_4 is true since in Link State Algorithms every node broadcasts it’s neighbours information to all the other nodes. But in Distance Vector, each node sends routing information only to its immediate neighbours. So the number of network messages required in DV is less than LS.
Therefore option (D) is correct.

This explanation is provided by Chirag Manwani.

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