Difference Between Link State and Distance Vector

Link State vs Distance Vector

Distance vector protocol and Link state protocol are two major sections in routing protocols. Each routing protocols belongs to one or both of them. Routing protocols are used to learn about it’s neighbors, network changes, and routes in a network. In routing protocol where we use distance vector routing algorithm, the information about the connected routers is advertised periodically, ex: RIP sends updates about the network every 30 seconds. RIP V1, RIP V2, and IGRP are distance vector protocols. But in link state, routing protocols updates the network only when a change in network happens, and it is created to overcome the drawbacks of distance vector protocol. If the network is stable, link state protocol re-floods each LSA regularly, ex: OSPF advertises LSA every 30 minutes. OSPF and IS-IS can be recognized as Link state protocols. The messages containing information about the network are called LSA (Link State Advertisements). Here, all routers learn the same information about all routers and subnets in a network. This information is stored in RAM of a router and it’s called Link State Database (LSDB). In every router, they have an identical copy of the LSDB in memory.

Distance Vector Protocol

Although it’s rather disadvantages to use in larger networks, still Distance vector protocol like RIP is used in many individual networks, which helps to make internet. Distance vector routing protocols send periodic full routing updates, but sometimes, these full updates are limited by split-horizon, which is used as a loop prevention mechanism. Split horizon does not let a route to be advertised to the same interface where the route is generated. When a router fails, it sends an immediately triggered message, which is called a triggered update. After a router learns about a failed route, it suspends split-horizon rules for that route and advertises a failed route and removes it from the network. When a route is down, every router is given a time called hold down timer to know about that failure, and it to be removed.

Link State Protocol

In link state routing protocol, every node constructs a map of every connectivity around a router. Every router has full knowledge on to which router it’s connected, and they add best routes to their routing tables based on metric, at last, every router in the internetwork has the same information about the internetwork. When considering with Distance Vector protocol, Link state protocol provides fast convergence, and it reduces the possibility of creating loops in a network. Link state protocols do not need to use a large variety of loop preventions mechanisms. Link state protocols consume much more CPU and memory, but when a network is properly designed, this can be reduced. Therefore, it requires much more planning than distance vector protocol, and it is needed to use more configurations for a better network design.

What is the difference between Link State and Distance Vector?

· Distance vector protocols are used in small networks, and it has a limited number of hops, whereas Link state protocol can be used in larger networks, and it has unlimited number of hops.

· Distance vector protocol has a high convergence time, but in link state, convergence time is low.

· Distance vector protocol periodically advertise updates, but link state advertises only new changes in a network.

· Distance vector protocol advertises only the directly connected routers and full routing tables, but link state protocols only advertise the updates, and flood the advertisement.

· In distance vector protocol, loop is a problem, and it uses split horizon, route poisoning and hold down as loop preventing techniques, but link state has no loop problems.