) such as Open Shortest Path First (OSPF), Exterior Gateway Protocol (EGP), and Border Gateway Protocol (BGP). Internet Basics Several processes are involved in router operation. First, the router creates a routing table to gather information from other routers about the optimum paths. As discussed in Chapter 6, "Local Area Networking," routing tables can be static or dynamic; dynamic routing tables are best because they adapt to changing network conditions. Next, when data is sent from a network host to a router, on the way to its destination, the router examines the destination address in the IP header to determine the most efficient path to the destination. Routing protocols consider various metrics, including distance and cost, when computing the best path. The following sections discuss the various routing protocols, including distance- vector and link-state protocols, interior routing protocols, and exterior routing protocols. Distance-Vector Versus Link-State Protocols Two main types of routing proto- cols are involved in making routing decisions: distance-vector and link-state rout- ing protocols. Distance-vector routing protocols require that each router simply inform its neighbors of its routing table. Routers periodically flood a table of vectors. (A vec- tor is destination, distance, interface, and next hop.) Other routers receive the table, add their local costs, and calculate the forwarding table. For each network path, the receiving router picks the neighbor advertising the lowest cost, and then the router adds that into its routing table for readvertisement. Common distance- vector routing protocols are RIP (implementations of which exist both for IP and for Novell's Internetwork Packet Exchange [IPX]), AppleTalk Routing Table Main- tenance Protocol (RTMP), and Cisco's Interior Gateway Routing Protocol (IGRP). Link-state routing protocols control the routing process and enable routers to respond quickly to changes in the network. Link-state routing determines path lengths by using algorithms that 