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GATE 2011 CS (CS1) – Question 62

Computer Networks · Routing: Distance Vector and Link State Routing · 2 marks · Multiple choice

A symmetric five-node distance-vector network has links N1–N2=1,N2–N5=3,N5–N4=4,N4–N3=2,N2–N3=6. Stable vectors in N1,…,N5 order are 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 round exchanges current vectors, then updates; link-cost changes immediately affect only the incident nodes’ corresponding entries. N2–N3 decreases to two. After the next update round, what is N3’s vector?

Diagram for GATE 2011 CS (CS1) question 62
  1. (3,2,0,2,5)
  2. (3,2,0,2,6)
  3. (7,2,0,2,5)
  4. (7,2,0,2,6)

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Show answer and explanation

Correct answer: (A) (3,2,0,2,5)

Explanation

N3 has neighbours N2 at cost two and N4 at cost two. Using their advertised vectors, distance to N1 is min(2+1,2+8)=3; N2=2; N4=2; N5=min(2+3,2+4)=5. Its self-distance is zero. Thus (3,2,0,2,5), A.

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