general conceptual doubt

Question

In distance vector routing while calculating the minimum distance do we also compare with the value present in the old table?? or we just check the values from the neighboring tables which are shared and check the minimum among them for calculating the new distance vector??

Comments

just compare what u r getting from other nodes. old table is not used

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We check perticular node [old values] with neighbour's shared table value if distance is minimum then update otherwise take old value.

Answer 1

actually suppose we need to find new routing table for A....for A to B value in the new table we will find

min {A->B + B to B
       A->D + D to B}...suppose B,D are neigbours of A

NOTE:    -> means in one hop ....to means more than one hop

now to calculate A->B and A->D(above) we use previous values of A's routing table which were known and B to B and D to B are calculated through new obtained routing tables.....

Comments

I have also followed the same methods but in forouzan i got to read that we also compare with the old table and check which one is smaller. But in tanenbaum its clearly written that old table is not used for calculation. Thats why i m confused.

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can u post that screenshot or any solved example from tanenbaum based on that method..because AFAIK it's done this way only..

we are not using old table here...for new routing tables recieved distance vectors are only used but A will always know whats its distance to its immediate neighbour's..