3Com Router 3000 Ethernet FamilyConfiguration Guide Chapter 1 IP Routing Protocol Overview3Com Corporation1-310.0.0.011.0.0.012.0.0.013.0.0.014.0.0.015.0.0.016.0.0.0R8210.0.0.1111.0.0.1313.0.0.4R2R3R5R6 R7R1 R410.0.0.216.0.0.316.0.0.116.0.0.213.0.0.315.0.0.115.0.0.214.0.0.114.0.0.213.0.0.213.0.0.112.0.0.112.0.0.212.0.0.3Routing table of Router R8DestinationNetwork10.0.0.0Nexthop Interface10.0.0.1 211.0.0.0 11.0.0.1 112.0.0.0 11.0.0.2 211.0.0.213.0.0.0 13.0.0.4 314.0.0.0 13.0.0.2 315.0.0.0 10.0.0.2 216.0.0.0 10.0.0.2 2Figure 1-2 Routing tableA router supports the configuration of static route as well as a series of dynamic routingprotocols such as RIP, OSPF, IS-IS and BGP. Moreover, a router in operation canautomatically obtain some direct routes according to interface state and userconfiguration.1.2 Routing Management PolicyYou can manually configure a static route to a certain destination, or configure theinteraction between dynamic routing protocol and other routers in the network and findroute via routing algorithm. The static routes configured by the user are managedtogether with the dynamic routes discovered by the routing protocol in the router. Thestatic routes and the routes learned or configured by different routing protocols can alsobe shared among routing protocols.1.2.1 Routing Protocols and Route Discovery PreferenceDifferent routing protocols (including static routes) may discover different routes to thesame destination, but not all these routes are optimal. In fact, at a certain moment, onlyone routing protocol can determine the current route to a specific destination. Thus,each of these routing protocols (including static routes) is assigned with a preference.When there are multiple routing information sources, the route learned by the routingprotocol with the highest preference will become the current route. Table 1-1 lists therouting protocols and the default preferences (the smaller the value, the higher thepreference is) of the routes discovered by them.
