Although RIP was a big step up from having to program routes in manually, it did not scale very well in medium- and large-sized networks. Convergence and routing loops were also a factor with RIP. For those reasons, OSPF has probably become the most widely implemented routing protocol for internal networks. There are other proprietary routing protocols which have also been popular, but they do not offer the same possibilities to integrate with such a wide range of platforms.

OSPF is a link state routing protocol, and works very differently than RIP. Every OSPF router announces the routes that it connects to, and all other OSPF routers are given the same information via multicast. This allows every router to have a picture of the whole network, instead of just knowing about your neighbor. The bird s eye view that OSPF has on a routing domain helps protect it from being subjected to routing loops like its distance vector cousin. That isn t to say you can t mess up an OSPF implementation, just that there are certain safeguards built in to the protocol itself.

OSPF also offers more segmentation and scalability than other distance vector routing protocols. In this section, we will begin by explaining the key concepts and terminology of OSPF. We will then move onto the implementation of OSPF in the firewalls, and include some examples.