Routing Fundamentals

To begin, you need to understand the routing function itself and what happens during the
process. In this section, I show you how a router makes its decisions about where and how
to send data. You’ll learn about the information that a router needs in order to make these
decisions. Then you’ll delve into the ways that the router gets this information—both static
routing (you, as the administrator, will give this to the router) and dynamic routing. You will
look at administrative distance and some of the functions that help a router determine which
routing information is the best. You will see how dynamic routing protocols are categorized
and the features each provides.

Basic Routing :

At this point we have discussed connecting hosts and wiring up the network for use. With
routing, you go beyond the network connections. You have figure out how the router is
going to pass data between subnets. Start off by thinking about the information a router
needs to make a routing decision. Routers care only about networks when they are routing,
not about individual host IP addresses. Every router must know about every destination network to which it can send data. If a router has a packet to route but the destination network
is not in its routing table, then the packet will be dropped.

The information that a router needs to route are:

• NN Destination address
• NN Possible routes to all remote networks
• NN The best route or path to a destination network
• NN Neighbor routers from which it can learn routes and send data
• NN A way to learn, update, and maintain route information