Hour 15: Distance Vector vs Link State analogy

One of the questions people new to networking often ask me is the difference between Distance Vector routing and Link State routing. There are many differences between them and you can research the details if you’d like to but I like to use two analogies to explain them. Here they are:

Distance Vector Routing: You are wandering in the Banff mountains of northern Alberta in Canada, a wonderful place to wander if you aren’t lost. But you are lost. You come upon a fork in the trail and you see a sign pointing west, reading “Edmonton 140km”. You have no choice but to trust the sign. You have no clue how the terrain is for the next 140km and you don’t know whether there is a better route or even if the sign is correct. In similar way, distance vector protocols provide road signs to networks. They provide the direction and the distance, but no details about what lies along the route.

Link-state Routing: You are in the biggest mall in Canada; the West Edmonton mall. You need to get to a computer store. You find the map of the mall and there’s a “you are here” dot on it, indicating where you are. From there you plan your way to the nearest computer store.

Just like every map in the mall is the same, the link-state database is the same in all routers within an area of a link-state routing protocol. The one difference between all the maps in the shopping mall is the “you are here” dot and so, the best path to a specific store will be different from each location in the mall. Link-state routing functions the same way, it calculates the best way to every network within the area, from their own perspective, using its own map; the Link-State Database.

I hope you liked these analogies as they’ve been really helpful to me.

On a side note: today I received my Cisco 2511 Access Server. I need to make a couple of roll-over cables to connect them to my home lab. I’m still waiting on 2x NM-1FE-2W WIC modules to be delivered. I need these for my 3600’s series Frame Relay switching router because the NM-1E-2W version does not support WIC-2T interface cards. So be careful if you plan on purchasing a 3600’s series router as only the FE modules support the WIC-2T interface cards.


  1. Pingback: OSPF – iphub

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