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PYQs Session 2

Consider a ne...

Question

Consider a network (A, B, C, D, E, F) where distance vector routing is used. Router C has received the following vectors from B(3, 0, 6, 8, 4, 2), D(12, 13, 5, 0, 8, 10) and F(8, 9, 7, 4, 4, 0). Assume the cost of the links from C to B, D and F are 3, 2 and 1 respectively.
Which of the following will be C's routing table?

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Solution

Router C has recived routing table from B, D and F.

Going via B gives (3 + 3, 0 + 3, 6 + 3, 8 + 3, 4 + 3, 2 + 3) = (6, 3, 9, 11, 7, 5)

Going via D gives ( 12 + 2, 13 + 2 + 2, 5 + 2, 0 + 2, 8 + 2, 10 + 2) = (14, 17, 7, 2, 10, 12)

Going via F gives (8 + 1, 9 + 1, 7 + 1, 4 + 1, 4 + 1, 0 + 1) = (9, 10, 8, 5, 5, 1)

Taking the minimum for each destination (A, B, C, D, E, F) except for C is (6, 3, 0, 2, 5, 1) via

(B, B, -, D, F, F).

Hence (b) is the correct option.

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Similar questions

Q. Consider a network having 6 nodes A, B, C, D,E, F and the measured delay between A to B, A to D and A to C are 4,5,6 respectively. Which of the following is routing table of A using distance vecotr routing? The vector table of B, D, C are given follows

A B C D E F

Vector table of 'B' = (2, 0, 4, 4, 3, 2)
Vector table of 'C' = (5, 4, 0, 2, 7, 4)
Vector table of 'D' = (5, 1, 3, 0, 3, 6)

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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.
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Q. Consider a network with five nodes, N1 to N5, as shown below.

The network uses a Distance Vector Routing protocol. Once the routes have stabilized, the distance vectors at different nodes are as following.
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N2: (1, 0, 6, 7, 3)
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Q. Consider a network with 6 routers R1 to R6 connected with links having weights as shown in the following diagram.

All the router use the distance vector base routing algorithm to update their routing tables. Each router starts with its routing table initialized to contain an entry for each neighbour with the weight of the respective connecting link.
After all the routing tables stabilize, how many links in the network will never be used for carrying any data?

Q. Consider a network with five nodes, N1 to N5, as shown below.

The network used a Distance Vector Routing protocol. Once the routes have stabilized, the distance vectors at different nodes are as following.
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 distance vector is the distance of the best known path at that instance to nodes, N1 to N5, where the distance to itself is 0. Also, all links are symmetric and the cost is identical in both directions. In each round, all nodes exchange their distance vectors with their respective neighbors. Then all nodes update their distance vectors. In between two rounds any change in cost of a link will cause the two incident nodes to change only that entry in their distance vectors.

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\infty

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