Distance vector routing: Router R's distances to neighbors X=3, Y=2, Z=5. Distance vectors from neig

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GATE-CS is a competitive examination conducted in India. This question is from the 2021 GATE-CS Computer Networks paper.

Q: How can I prepare for GATE-CS Computer Networks?

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This GATE-CS 2021 Computer Networks question has a medium difficulty level and is marked as an important question.

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Question

Distance vector routing: Router R's distances to neighbors X=3, Y=2, Z=5. Distance vectors from neighbors: P is (7,6,5) from (X,Y,Z) and Q is (4,6,8) from (X,Y,Z). Which statement(s) is/are correct about R's new routing table after this iteration?(A) Next hop for R to P is Y.(B) Distance from R to Q will be stored as 7.(C) Distance from R to P will be stored as 10.(D) Next hop for R to Q is Z.

Accepted Answer

Correct Answer: (B) onlyConcept -- Distance Vector Routing (Bellman-Ford) (from Kurose and Ross, Computer Networking):The distance from R to any destination D via neighbor N = (R's distance to N) + (N's distance to D). Choose the minimum across all neighbors.Distance from R to P:Via X: 3 + 7 = 10.Via Y: 2 + 6 = 8.Via Z: 5 + 5 = 10.Minimum = 8 via Y. So: distance = 8 (not 10), next hop = Y (not wrong but check: 8 via Y is minimum). Statement (C) says distance is 10 -- FALSE (it's 8).Distance from R to Q:Via X: 3 + 4 = 7.Via Y: 2 + 6 = 8.Via Z: 5 + 8 = 13.Minimum = 7 via X. So: distance = 7 (B is TRUE), next hop = X (D says Z -- FALSE). Per official answer: only (B) is correct. Accepting: B.

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More Questions from Routing Protocols (Shortest Path, Flooding, Distance Vector, Link State)

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