3Com 10014299 manual Configuring Static Routes, Default Route

27 CONFIGURING STATIC ROUTES

This chapter covers the following topics:

■Static Route Overview

■Configuring a Static Route

■Displaying and Debugging the Routing Table

■Static Route Configuration Example

■Troubleshooting a Static Route Configuration

Static Route Overview A static route is a special route that allows a router to transmit packets over one path to a specified destination. Proper setting and application of the static route can guarantee network security effectively and at the same time, ensure bandwidth for important applications.

If the topology changes due to network failure or other problems, the static route cannot change automatically and requires the intervention of administrator.

The static route has the following attributes:

■Reachable route: Normally all routes are reachable and an IP packet is sent to the next hop according to the route identified by the destination -- a common application of static routes.

■Unreachable route: When a static route to a certain destination has the "reject" attribute, all IP packets to this destination are discarded and destination unreachable information is given.

■Black hole route: When a static route to a certain destination has "black hole" attribute, all IP packets to this destination will be discarded.

Here, the attributes reject and blackhole are normally used to control the scope of destinations reachable by this router, to facilitate network fault diagnosis.

Default Route

Default route is one type of static route that is used when no matching route is found or when there is no suitable route. In the routing table, the default route is the route to network 0.0.0.0 (mask is 0.0.0.0). You can check whether the default route is properly set through the result of display ip routing-tablecommand. If the destination address of the message does not match any route item in the routing table, the default route is selected. If there is no default route, this message will be discarded and an ICMP message will be returned to the source terminal, indicating that the destination address or network is unreachable.