3Com 2928 User Guide - Page 299

1 Routing Configuration The term "router" in this document refers to a switch supporting routing function. Overview Routers are responsible for routing packets on the Internet. A router selects an appropriate route according to the destination address of a received packet and forwards the packet to the next router. The last router on the path is responsible for sending the packet to the destination host. Routing Table Routers forward packets through a routing table. Each entry in the table specifies which physical interface a packet should go out to reach the next hop (the next router) or the directly connected destination. Routes in a routing table fall 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. A route entry has the following items: z Destination IP address: Destination IP address or destination network. z Mask: Specifies, together with the destination address, the address of the destination network. z Outbound interface: Specifies the interface through which a matching IP packet is to be forwarded. z Nexthop: Specifies the address of the next hop router on the path. z Preference for the route: Routes to the same destination may be found by various routing protocols or manually configured, and routing protocols and static routes have different priorities configured. The route with the highest priority (the smallest value) will be selected as the optimal route. Static Route A static route is manually configured. If a network's topology is simple, you only need to configure static routes for the network to work normally. The proper configuration and usage of static routes can improve network performance and ensure bandwidth for important network applications. The disadvantage of using static routes is that they cannot adapt to network topology changes. If a fault or a topological change occurs in the network, some routes will be unreachable. In this case, the network administrator has to modify the static routes manually. 1-1