GATE CS 2021 Set 2 — Question 55
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Computer Networks → Network Layer: Routing → Distance Vector Routing
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Question
Consider a computer network using the distance vector routing algorithm in its network layer. The partial topology of the network is as shown below.
The objective is to find the shortest-path path from the router to routers and . Assume that does not initially know the shortest routes to and . Assume that has three neighbouring routers denoted as , , and . During one iteration, measures its distance to its neighbours , , and as , , and , respectively. Router gets routing vectors from its neighbours that indicate that the distance to router from routers , , and are , , and , respectively. The routing vector also indicates that the distance to router from routers , , and are , , and , respectively. Which of the following statement(s) is/are correct with respect to the new routing table of , after updation during this iteration?
Correct answer
(B) The distance from R to Q will be stored as 7.; (C) The next hop router for a packet from R to P is Y.
Solution
In distance vector routing, the distance to a destination from router is updated as:
Given distances to neighbors:
For destination P:
The minimum is achieved via neighbor . So, distance is 8 and next hop is .For destination Q:
The minimum is achieved via neighbor . So, distance is 7 and next hop is .Evaluating options:
(A) Distance to is 8, not 10. (False)
(B) Distance to is 7. (True)
(C) Next hop for is . (True)
(D) Next hop for is , not . (False)
Given distances to neighbors:
For destination P:
The minimum is achieved via neighbor . So, distance is 8 and next hop is .For destination Q:
The minimum is achieved via neighbor . So, distance is 7 and next hop is .Evaluating options:
(A) Distance to is 8, not 10. (False)
(B) Distance to is 7. (True)
(C) Next hop for is . (True)
(D) Next hop for is , not . (False)
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