OSPF is a commonly implemented link-state routing protocol. It was developed as a replacement for the distance vector routing protocol, RIP. However, OSPF has significant advantages over RIP in that it offers faster convergence and scales to much larger network implementations.
OSPF features, as shown in the figure, include:
- Classless - It is classless by design; therefore, it supports VLSM and CIDR.
- Efficient - Routing changes trigger routing updates (no periodic updates). It uses the SPF algorithm to choose the best path.
- Fast convergence - It quickly propagates network changes.
- Scalable - It works well in small and large network sizes. Routers can be grouped into areas to support a hierarchical system.
- Secure - It supports Message Digest 5 (MD5) authentication. When enabled, OSPF routers only accept encrypted routing updates from peers with the same pre-shared password.