MadeEasyTestSeries:CN-Distance Vector Routing

Question

Comments

@ Shubhanshu

The x value :

In exchange 1 Q to R

In exchange 2 R to S

In exchange 3 R to Q

In exchange 4 Q to P 

so x = 4

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thanks sir I am also getting 'x= 4
but what should be y?

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@student2018

Also here is NO 'count to infinity' problem as it is mention in question 

Assume all routers exchange message at the same time 

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and here y=7 see this how it is :

In exchange 1 P to Q

In exchange 2 Q to R

In exchange 3 R to S

In exchange 4 Q to R

In exchange 5 R to S

In exchange 6 R to Q 

In exchange 7 S to Q

so y value = 7

Answer 1

The x value :

In exchange 1 Q to R

In exchange 2 R to S

In exchange 3 R to Q

In exchange 4 Q to P

so x = 4

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The y value :

In exchange 1 P to Q

In exchange 2 Q to R

In exchange 3 R to S

In exchange 4 Q to R

In exchange 5 R to S

In exchange 6 R to Q

In exchange 7 S to Q

so y value = 7

x=4 & y=7 , option D .

Comments

At  3rd Exchange, the table for Q look like this :

Dest	HopCount	Next
P	1	-
R	1	-
S	2	R

For P after 4th exchange table will look like : 

Dest	HopCount	Next
Q	1	-
R	2	Q
S	3	Q

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Sir, acc to Forouzan, the next entry in Q's table for P and R will be Null or "-" because there is no next node between Q and P or Q and R. 

Doubt 2) In P's table for entry Dest = S why next node = R why not Q because Q is next while going for S from P.

Doubt 3) Till 2nd Exchange the table of Q will be 

Dest	HopCount	Next
P	1	-
R	1	-
S	2	R

So in 3rd Exchange simply Q will forward this routing table to P, then routing table of P will become

Dest	HopCount	Next
Q	1	-
R	2	Q
S	3	R

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Doubt 2) In P's table for entry Dest = S why next node = R why not Q because Q is next while going for S from P.

yes, that was a typo, it should be Q not R.

so the table for P becomes after 4th exchange : 

Dest	HopCount	Next
Q	1	-
R	2	Q
S	3	Q