Distance Vector vs Link State - question about updates...

[chrisnrach17]

can anyone clarify the following (taken from the icnd book by odom):

"When a distance vector protocol in a router receives a routing update, the update says nothing about the routers beyond the neighboring router that sent the update. Conversely, link-state protocols advertise a large amount of topological information about the network, and the routers perform some CPU-intensive computation on the topological data."

- I thought that when a distance vector protocol receives an update it DOES give details about routers beyond the neighboring router - i.e. all the routes that the neighboring router has learnt.

can anyone clarify this for me?

thanks

[mohammedmahmoud]

Hi,

The idea is in the algorithm that each uses, in the case of Link State protocols, Dijkastra algorithm builds a topology database (which must be identical on all routers in the same area), and so each router must send information about the routers beyond it (actually its sends its link states with the neighboring routers over them).

On the other hand in the distance vector protocol (Bellman-Ford Algorithm) the router only anounces the networks which it can reach with no information about any routers beyond it.

Hope that helps,

Mohammed.

[Richard Burts]

Chris

I think that Mohammed has got us started with some useful information about distance vector and link state protocols. I believe the answer to your question is to be clear about the subtle difference in advertising information about routes and advertising information about routers. You are correct that distance vector protocols advertise information about remote routes but they do not advertise information about remote routers. The distance vector protocol will tell that some remote network (or subnet) exists and is reachable, but it does not tell us anything about what router that network is connected to. Link state protocols do tell us that.

HTH

Rick

[chrisnrach17]

ah the penny's just dropped. that's explained it better than any book i've read Rick.

thanks for your responses. spot on!

[Richard Burts]

Chris

I am glad that my answer helped you understand the concept. I encourage you to continue your participation in the forum.

HTH

Rick