Distance Vector

Question

This is a snapshot from tanenbaum.

What i learned from highlighted text is:- " Suppose a node A has Neighbours B and C. B and C will share its Vector with A after a specific duration of time and suppose C's Vector reaches first to A cuz distance to A is smaller than A to B(say),and Suppose C provides me Distance to a node x (which was latest introduced).Now when B's vector will come then i will change my routing vector only if B's Routing vector specifies a field with less distance then what i already have(yea by calculating from my position)"

Am i right?

Comments

Let suppose you're node A. and currently you have cost 'x' to reach a node P , now from your neighbor B you receive it's routing table and then what you will do ? you will check if by this neighbor B , can i reach node P more early. mathematically you will check whose is greater b/w 'x' and D_B+D_B->P.

if you can reach node P from B then you will update your entry to reach node P.

Now let suppose you have new entry to reach node P , which is D_B+D_B->P But after some time you again receive update from same node B to reach P , it's new value this time , so this time , without any compare you will just update the cost with new cost. because if you're reaching P from B and now B is giving you new cost , then it just mean , we have new path to reach P from B , may be old path is broken.

https://inst.eecs.berkeley.edu/~cs168/fa14/discussion/handout2-ans.pdf

you can read routing protocols from forouzan.

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Sir I have a doubt please clear me

Three nodes A,B and C , A is connected to B and C directly Currently In A.s Table The distance to say node X is P which was given by C, B also gave a distance to X say Q but Q>P so A chooses to go with C earlier.

Now sir Something Happened and distance to X from C has Changed to P1,now C advertises it to A,Since distance to X in A's table was by C so A needs to Consider the new distance but Suppose if B gives a distance to X as Q and Q<X1. So will A now abandon C and go with B? and update distance according to B?

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This is all , what routing protocols do. Let suppose we are working with RIPv1 protocol , so what does it do? time by time node sends their routing tables to their neighbors , and this process keep on going.

in your question , i'm supposing your mean by cost P is AC+CX and Q=AB+BX , so now if when P changes to p1 , and then whenever node B sends it's routing table to node A , same process will happen , A will check if there is possibility to reach some destination with less cost than it's current entries using B. if yes then it will update.

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Thank you sir got it