Static routing allows a network administrator to program the router with specific delivery rules. One such rule might be that all out-bound packets, regardless of their destination address, be sent to the Internet Service Provider's routers for further delivery. Another rule might be that any packets destined for the 192.168.1 network be forwarded to the Ethernet LAN segment, while packets for 192.168.2 be forwarded to the Token Ring LAN segment.
By using static routing rules, the network administrator is eliminating the need for the routers or the systems on the network to learn anything. However, this also robs the network or flexibility in case addresses or network numbers change. If the address of the locally-defined router is changed, or if another router is promoted to act as the default router, then each and every system on the local network must be reconfigured with this information. This adds a lot of overhead to the network management function, even in small installations.
There are several routing protocols that can monitor the state of the network itself, allowing systems to adjust to router changes dynamically. The two most common of these protocols are RIP and OSPF. For more information on RIP, refer to section B.4.2 Routing Information Protocol (RIP). For more information on OSPF, refer to section B.4.3 Open Shortest Path First (OSPF).
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