CISCO IOS in a Nutshell

OSPF

OSPF (Open Shortest Path First) is a link-state protocol. It’s a good choice for networks that need a more sophisticated routing protocol than RIP but are not willing to standardize on a single router vendor, and therefore have problems using EIGRP. It has a number of significant advantages, most of which it shares with EIGRP: it doesn’t use a lot of network bandwidth, it supports VLSM, and it converges quickly when the network’s state changes. Its biggest advantage over EIGRP is that it is an open standard and is supported by almost all router vendors.

OSPF has a reputation for being very complex, and to some extent, this reputation is deserved. However, in small networks it can be configured quickly. This book does not give a comprehensive look at OSPF or its capabilities.

As you’ll see, OSPF forces you to use a certain topological design. OSPF divides your network into areas; area 0 is the “backbone” to which all other areas must connect. While this design fits many (perhaps even most) networks, and while there are some tools for giving you additional flexibility, you might reasonably object to using a routing protocol that limits your network’s flexibility in the future. However, some people feel that this aspect of OSPF is an advantage, as it forces the use of decent network-design practices.

One possible disadvantage of OSPF is that it tends to use a lot of CPU time on the router because the OSPF LSA maintenance algorithms are CPU-intensive. This tendency to be a CPU ...