There are two major differences between Distance Vector routing protocols and Link State routing protocols. Distance Vector exchanges the routing updates periodically whether the topology is change or not, this will maximize the convergence time which increases the chance of routing loops while the Link State routing protocols send triggered change based updates when there is a topology change. After initial flood, pass small event based triggered link state updates to all other routers. This will minimize the convergence time that’s why there is no chance of routing loops. Secondly, the Distance Vector routing protocols rely on the information from their directly connected neighbours in order to calculate and accumulate route information. Distance Vector routing protocols require very little overhead as compared to Link State routing protocols as measured by memory and processor power while the Link State routing protocols do not rely solely on the information from the neighbours or adjacent router in order to calculate route information. Instead, Link State routing protocols have a system of databases that they use in order to calculate the best route to destinations in the network. An extra feature of Link State routing protocol is that they can detect media types along with other factors. This could increase the overhead as compare to Distance Vector routing protocols in order to measure by processor power and memory. Routing Information Protocol (RIP) and Interior Gateway Routing Protocol (IGRP) are the examples of Distance Vector routing protocols while the Open Shortest Path First (OSPF) is a classic example of Link State routing protocols.
The other differences of both types of routing protocols are as follows:
- Distance Vector routing protocols are based on Bellma and Ford algorithms.
- Distance Vector routing protocols are less scalable such as RIP supports 16 hops and IGRP has a maximum of 100 hops.
- Distance Vector are classful routing protocols which means that there is no support of Variable Length Subnet Mask (VLSM) and Classless Inter Domain Routing (CIDR).
- Distance Vector routing protocols uses hop count and composite metric.
- Distance Vector routing protocols support dis-contiguous subnets.
- Common distance vector routing protocols include: Appletalk RTMP, IPX RIP, IP RIP, IGRP
- Link State routing protocols are based on Dijkstra algorithms.
- Link State routing protocols are very much scalable supports infinite hops.
- Link State routing protocols are classless which means that they support VLSM and CIDR.
- Cost is the metric of the Link State routing protocols.
- Link State routing protocols support contiguous subnets.
Limitations of Distance Vector
For Distance Vector routing protocols such as RIP, IGRP as well as hybrid routing protocols with the characteristics of Distance Vector such as EIGRP while maintaining routing information, the routing loops have been occurred. It is because the Distance Vector routing protocols send periodic routing updates and each node maintain the distance from itself to each possible destination network, for this the convergence time of Distance Vector routing protocols is slow. Slow convergence produces inconsistent routing. When the topology of network changes and a network has gone down, the packets for the network bounce between routers and the hop count for specific network counts to infinity, the solution is split horizon. Split horizon follows the rule that it is never useful to send information about a route back in the direction from which the original packet came. Split horizon can be disabled for all Distance Vector routing protocols.
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