Today we see the different types of routing tables. We see where each type find extensive application.
If an intranet has only a limited number of other TCP/IP networks, then a static routing table can be used. In this case, packets with specific addresses are sent to specific routers-the routers do not redirect packets to adjust to changing network traffic. Static routing should be used when there is only one route to each given destination. A static routing table allows an intranet administrator to add or take away entries in the routing table.
Dynamic routing tables are the most sophisticated routing tables. They should be used when there is more than one way in which data can be sent from a router to the final destination, and in more complex intranets. These tables constantly change as network traffic and conditions change, so that they always route data the most efficient way possible, taking into account the current state of traffic on the intranet.
Dynamic routing tables are built using routing protocols. These protocols are ways in which routers communicate with one another, giving each other information about the most efficient way of routing data given the current state of the intranet. A router with a dynamic routing table can automatically switch data to a backup route if the primary route is down. It can also always determine the most efficient way of routing data toward its final destination. Routers advertise their IP addresses and know the IP addresses of their neighbors. Routers can use this information in an algorithm to calculate the best route to send packets.
The most common routing protocol that performs these best-case calculations is known as RIP (Routing Information Protocol). When RIP determines the most efficient route for data, it calculates the hop count for the route. RIP always chooses the path with the lowest hop count as the route to send data over. It assumes that the fewer the hops, the more efficient the path. RIP will not allow any path with a hop count of over 16. If there is a hop count of over 16, it will discard the route. On most intranets this shouldn't be a problem.
The Exterior Gateway Protocol (EGP) is used for the Internet where many more routers might have to be traversed before a packet reaches its final destination. It will not be needed on an intranet since it's rare that an intranet would be so large that data would have to pass through more than 16 routers or gateways in order to be sent to the final destination.
