Difference between Link-State and Distance Vector

Ok, so we've all memorized what interior routing protocols are Link-State and which are distance vector, but what does that mean exactly?


Well, the biggest difference is the view of the network that each router has.

In a Distance Vector protocol, routers only see their neighboring routers, and only see the "distance" or cost passed to it from each "vector" or direction. In other words, a distance vector router sees a list of x routes with a cost on interface 1 and y routes with costs on interface 2.

Link-State protocols on the other hand use a bit more overhead and processing power. With a link state router, the entire (area or domain) topology is known by every router.

Picture it like this, Distance Vector is sitting at an intersection seeing the signs, turn left = 2000 miles to NY, Turn right = 1000 miles to portland, continue straight = 1700 miles to Dallas. All you have are distances and an arrow, you have no idea how straight or round-about the path may lead.

Link state is when you are looking at a map. You can see that turning left does indeed take you toward NY, but can see a slew of different roads and freeways that you can choose from. You make your own decision based on the entire topology of the road system.

The other difference between the two protocols is that link state sends advertisements only when a link changes, so if a router sees a link go up or down, it sends the changes.

Distance Vector sends regular announcements of it's paths and costs at a set time interval.