Distance vector vs Link state

Unanswered Question
Apr 12th, 2009

I am preparing my 350-001. Here is a sample question. Which one do you think is the correct answer?

You are deciding which routing protocol to implement on your network. When weighing the different options, which of the following are valid considerations?

A. Distance vector protocols have a finite limit of hop counts whereas link state protocols place no limit on the number of hops.

D. Distance vector protocols only send updates to neighboring routers. Link state protocols depend on flooding to update all routers in the within the same routing domain.

The answer is A but I rather chose D. Is EIGRP a Distance vector protocol? Does it have a finite limit of hop counts? Also, I think Link state protocol should flood updates to all routers within the same routing domain. I know OSPF only flood within an area but it's not technically a Link state protocol anymore between areas. It's more like a Distance vector protocol between areas. I think strict link state protocol should be just like OSPF with only one area.

Any opinions are welcome! Thanks!


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Overall Rating: 1.4 (5 ratings)
scottmac Sun, 04/12/2009 - 18:34

IGRP and EIGRP are cnsidered "hybrid" routing protocol because it has some aspects of link state and some aspects of a distance vector routing protocol.

Good Luck

Difan Zhao Mon, 04/13/2009 - 08:18

So distance vector protocol does have a limit hop count? Why link state protocol doesn't have a hop count limit?


I think you are missing the difference.

Link state protocols maintain a topology database. The master DR maintains this an replicates the information. All devices share the same database.

Distance vector tell their neighbors about the routes they know about (that's the vector part). The updates have a limited TTL (RIPv1 was 15 hops) to contain the SCOPE of the routing updates.

The hop count is to Distance Vector protocols as areas are to Link State protocols. They limit scope.

The answer is D.

Answer A is WRONG.

Link state protocols do not use hop count.

jason.chilton Thu, 05/07/2009 - 14:04

Answer A is not wrong, because it states that distance vector protocols use a hop count. It never said that link state does.

Both A and D state correct facts about the protocols, but the question is not asking which one is right and which one is wrong, instead the question is asking you that if you are choosing a protocol, which of those listed facts should be taken into consideration in choosing your protocol.

When choosing a protocol, the fact that distance vector only advertises to neighbors while link state floods within a domain makes very little difference in choosing one over the other. However, the fact that you will be limited by a hop count if you choose distance vector could be a very important consideration in choosing one over the other.


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