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40 votes
40 votes

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

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

  1. $0$
  2. $1$
  3. $2$
  4. $3$

 

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8 Answers

Best answer
48 votes
48 votes

First we need to find which are the unused links in the graph
For that we need not make distance vector tables,
We can do this by simply looking into the graph or else DVT can also give the answer.
So, $R1-R2$ and $R4-R6$ will remain unused.

Now If We changed the unused links to value $2$.
$R5-R6$ will Now remain unused.

So, the correct answer is option B).

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26 votes
26 votes

Only one link is not used

8 votes
8 votes
Option-B

SImple reason for this.Use your intuition like below way

Find all the shortest path from each node to other and mark your visited edge .Then automatically in first searching u will find that only two edge are unused example edge R1---->R2 as well as R4---->R6.

When u change it into 2,Then again apply your intuition to find out shortest path from each node to other in this satuation u again find on link is unused.
7 votes
7 votes

The links R1-R2  and R4-R6 will never be used for data transfer because there are shorter paths available in any case.
If those two link weights are changed to 2, now only one link ie R5-R6 will never be used.

Answer:

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