Hybrid Routing

In a hybrid routing scheme, some parts of the network use static routing, and some parts use dynamic routing. Which parts use static or dynamic routing is not important, and many options are possible. One of the most common hybrid schemes is to use static routing on the fringes of the network (what I have called the access networks) and to use dynamic routing in the core and distribution networks. The advantage of using static routing in the access networks is that these networks are where your user machines are typically located; these machines often have little or no support for dynamic routing. Additionally, access networks often have only one or two router attachments, so the burden of configuring static routing is limited. It may even be possible to define nothing more than a default route on these stub networks. Because of the limited connections to these networks, you usually don't need to reconfigure routing on a stub network when it gets moved to a new place in the network.

On the other hand, distribution and core networks often have many router connections, and therefore many different routes to maintain. Therefore, routers in these components of the network usually can't get by with a default route. Routers (and hosts) in the central parts of the network need complete routing information for the entire network. Furthermore, routers in the core and distribution networks usually need to be informed of changes in the connectivity of access networks. While it is certainly possible to inform each router manually when an change occurs, it is usually easier and more practical to allow a dynamic routing protocol to propagate the changes.