# GATE Questions & Answers of Routers and Routing Algorithms (Distance Vector, Link State)

## What is the Weightage of Routers and Routing Algorithms (Distance Vector, Link State) in GATE Exam?

Total 7 Questions have been asked from Routers and Routing Algorithms (Distance Vector, Link State) topic of Computer Networks subject in previous GATE papers. Average marks 1.71.

Consider the following statements about the routing Protocols, Routing Information protocol (RIP) and open shortest path First (OSPF) in an IPv4 network.

I. RIP uses distance vector routing

II. RIP packets are sent using UDP

III. OSPF packets are sent using TCP

IV. OSPF operation is based on link-state routing

Which of the statement above are CORRECT?

Assume that source S and destination D are connected through two intermediate routers labeled R. Determine how many times each packet has to visit the network layer and the data link layer during a transmission from S to D.

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

The network uses a Distance Vector Routing Protocol.once the Route 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 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 the 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.

The cost of link N2-N3 reduces to 2 (in both directions). After the next round updates, what will be the new distance vector at node, N3?

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

The network uses a Distance Vector Routing Protocol.once the Route 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 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 the 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.

The cost of link N2-N3 reduces to 2 (in both directions). After the next round updates, what will be the new distance vector at node, N3?

At the update in the previous question ,the link N1-N2 goes down. N2 will reflect this change immediately in its distance vector as cost, $\infty$. After the NEXROUND of update, what will be the cost to N1 in the distance vector of N3?

Consider a network with 6 routers R1 to R6 connected with links having weights as shown in the following diagram

All the routers use the distance vector based 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?

Consider a network with 6 routers R1 to R6 connected with links having weights as shown in the following diagram

All the routers use the distance vector based 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?

Suppose the weights of all unused links in the previous question are changed to 2 and the distance vector algorithm is used again until all routing tables stabilize. How many links will now remain unused?