# Distance Vector Routing Example

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

The network uses a Distance Vector Routing protocol. Once the routes have been stabilized, the distance vectors at different nodes are as follows.

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, N1toN5, 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.

It’s a GATE-2011 question.

I have a doubt here.

Suppose when the cost of the link N2-N3 changes to 2, this will be immediately known to N2 and N3 and they will update their routing table entry to reflect this change. Now, this would cause triggered update.

Suppose After receiving the vector from N2, N3 finally changes it’s vector to (3,2,0,2,5).

Now my query is whether this vector (3,2,0,2,5) would be communicated to N4 or the old vector of N3(7,6,0,2,6) would be communicated to N4?