Question
Consider Figure 4.31. Suppose there is another router w, connected to router y and z. The costs of all links are given as follows: c(x,y) = 4, c(x,z) = 50, c(y,w) = 1, c(z,w) = 1, c(y,z) = 3. Suppose that poisoned reverse is used in the distance-vector routing algorithm.
a. When the distance vector routing is stabilized, router w, y, and z inform their distances to x to each other. What distance values do they tell each other?
b. Now suppose that the link cost between x and y increases to 60. Will there be a count-to-infinity problem even if poisoned reverse is used? Why or
why not? If there is a count-to-infinity problem, then how many iterations are needed for the distance-vector routing to reach a stable state again? Justify your answer.
c. How do you modify c(y,z) such that there is no count-to-infinity problem at all if c(y,x) changes from 4 to 60?
Answer
a)
The cost of the network links from the given Figure 4.31:
n(x,z)=50
n(x,y)=4
n(y,z)=3
n(y,w)=1
n(z,w)=1
The distance values(D) do they tell each other as:
b)
Consider that the link cost between x and y increases to 60. Then there be a count-to-infinity problem even if poisoned reverse is used as routing converging process.
The routing converging process table follows:
c)
If the link between router at all if c(y,x) changes is removed then there is no count-to-infinity problem even if the cost of link changes from 4 to 60.