OSPF Characteristics

OSPF is a link-state protocol in which all routers in the routing domain exchange information and thus know about the complete topology of the network. Because each router knows the complete topology of the network, the use of the SPF algorithm creates an extremely fast convergence. Other key characteristics of OSPF are as follows:

• Provides routing information to the IP section of the TCP/IP protocol suite, the most commonly used alternative to RIP.
• Sends updates to tables only, instead of entire tables, to routers.
• Is a more economical routing protocol than RIP over time because it involves less network traffic.

OSPF is usually more efficient than RIP in exchanging routing information when a network is stable; however, for this rule to hold true, it depends on network events. For example, during an external convergence event, OSPF could flood more traffic than RIP. Consider that RIP carries 25 routes per update; on the other hand, OSPF floods a single LSA per external route that is affected by the convergence event. So, provided that you have a (relatively) stable environment, OSPF involves less traffic, and over time, it is statistically more economical than RIP. Using a single LSA per external route is inefficient, but OSPF was never designed to be an EGP. Therefore, OSPF/BGP deployment when large numbers of external routers are present.

Another popular type of dynamic routing protocol that is based on the Dijkstra SPF algorithm is IS-IS. The use of IS-IS versus OSPF has been hotly debated.