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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-cost path from the router R to routers P and Q. Assume that R does not initially know the shortest routes to P and Q. Assume that R has three neighbouring routers denoted as X, Y, and Z. During one iteration, R measures its distance to its neighbours X, Y, and Z as 3, 2, and 5, respectively. Router R gets routing vectors from its neighbours that indicate that the distance to router P from routers X, Y, and Z are 7, 6, and 5, respectively. The routing vector also indicates that the distance to router Q from routers X, Y, and Z are 4, 6, and 8, respectively. Which of the following statement(s) is/are correct with respect to the new routing table of R, after updation during this iteration ?

A.
The next hop router for a packet from R to P is Y.
B.
The distance from R to Q will be stored as 7
C.
The next hop router for a packet from R to Q is Z.
D.
The distance from R to P will be stored as 10.

Solution:

Answer: Option 1 and Option 2Explanation:given data R ? X3R ? Y2R ? Z5To Router PCostFrom7X6Y5ZTo Router QCostFrom4X6Y8Z Cost of R ? P = Min (R ? X + X ? P, R ? Y + Y ? P, R ? Z + Z ? P)Cost of R ? P = Min (3 + 7, 2 + 6, 5 + 5)Cost of R ? P = Min (10, 8, 10) = 8Cost of R ? P = 8 and next hop is Y.Cost of R ? Q = Min (R ? X + X ? Q, R ? Y + Y ? Q, R ? Z + Z ? Q)Cost of R ? Q = Min (3 + 4, 2 + 6, 5 + 8)Cost of R ? Q = Min (7, 8, 13)Cost of R ? Q = 7 and next hop is X.

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