1-11 IP Routing Protocol OverviewGo to these sections for information you are interested in:z Introduction to IP Route and Routing Tablez Routing Protocol Overviewz Displaying and Maintaining a Routing TableThe term router in this chapter refers to a router in a generic sense or an Ethernet switch running arouting protocol.Introduction to IP Route and Routing TableIP RouteRouters are used for route selection on the Internet. As a router receives a packet, it selects anappropriate route (through a network) according to the destination address of the packet and forwardsthe packet to the next router. The last router on the route is responsible for delivering the packet to thedestination host.Routing TableFunctionThe key for a router to forward packets is the routing table. Each router maintains a routing table. Eachentry in this table contains an IP address that represents a host/subnet and specifies which physicalport on the router should be used to forward the packets destined for the host/subnet. And the routerforwards those packets through this port to the next router or directly to the destination host if the host ison a network directly connected to the router.Routes in a routing table can be divided into three categories by origin:z Direct routes: Routes discovered by data link protocols, also known as interface routes.z Static routes: Routes that are manually configured.z Dynamic routes: Routes that are discovered dynamically by routing protocols.Routing entryEach routing entry in a routing table contains:z Destination: It identifies the address of the destination host or network of an IP packet.z Mask: Along with the destination address, it identifies the address of the network segment wherethe destination host or router resides. By performing a logical AND operation between destinationaddress and network mask, you can get the address of the network segment where the destination
