GATE CS 2022 Set 1 — Question 57
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Computer Networks → Network Layer: Routing → Distance Vector Routing
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Question
Consider a network with three routers P, Q, R shown in the figure below. All the links have cost of unity.
The routers exchange distance vector routing information and have converged on the routing tables, after which the link Q−R fails. Assume that P and Q send out routing updates at random times, each at the same average rate. The probability of a routing loop formation (rounded off to one decimal place) between P and Q, leading to count-to-infinity problem, is___________.
Correct answer
0.5 to 0.5
Solution
In Distance Vector Routing, a routing loop (count-to-infinity) occurs if a router receives an update about a destination from a neighbor that was previously using that router to reach the same destination.Initially, the network is converged:
- is at distance 0 from .
- reaches via with cost 1.
- reaches via with cost 2.
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