In determining the best route to a destination, different routing protocols use a number of different measurements. These measurements are called metrics. Each routing protocol uses one or more metric to calculate the best route to a particular destination. The most common metrics include path length (hop count), reliability, delay, bandwidth, load, and financial cost of a link.
Another major difference between routing protocols is how they handle updating each other with current information. There are many methods of doing this. Given these major differences, routing protocols are broken into two main categories: Distance Vector and Link State.
Distance Vector protocols include RIP and IGRP. They send their entire routing tables out in all directions at regularly scheduled intervals.
Link State protocols are more advanced than distance vector protocols because, unlike distance vector, they do not send periodic routing updates. Link State protocols include OSPF, NLSP, BGP, and IS-IS.
They send partial routing tables (of their own networks) to everyone and then send updates when necessary.
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