affic, reliability, and security. So how does route information get into a routing table in the first place? The network administrator can manually enter the information in the router. Or, routers can learn the information, on the fly, from each other. Manual entries in routing tables are called "static routes". Routes learned automatically are called "dynamic routes". If routers can learn routing information automatically, it might seem pointless to manually enter information into a router's routing tables. However, such manual entries can be useful whenever a network administrator wants to control which path a router will select. For example, routing tables that are based on static information could be used to test a particular link in the network, or to conserve wide area bandwidth. Static routing is also the preferred method for maintaining routing tables whenever there is only one path to a destination network. This type of network is referred to as a stub network. There is only one way to get to this network, so it is important to indicate this situation to prevent routers from trying to find another way to this stub network if it's connection fails. Adaptive, or dynamic, routing occurs when routers send periodic routing update messages to each other. Each time a router receives a message containing new information, it recalculates the new best route, and sends the new updated information to other routers. By using dynamic routing, routers can adjust to changing network conditions. Before the advent of dynamic updating of routing tables, most vendors had to maintain router tables for their clients. This meant that vendors had to manually enter network numbers, their associated distances, and port numbers into the router tables of all the equipment they sold or leased. As networks grew larger, this became an increasingly cumbersome, time-consuming, and ultimately, expensive, task. Dynamic routing eliminates the need for networ...
