3Com 10014298 manual Default Route, Configuring a Static Route

Static Routes 85

Configuring Static Routes

■Unreachable route — When a static route to a destination has the reject attribute, all the IP packets to this destination are discarded, and the originating host is informed that the destination is unreachable.

■Blackhole route — When a static route to a destination has the blackhole attribute, all the IP packets to this destination are discarded, and the originating host is not informed.

The attributes reject and blackhole are usually used to control the range of reachable destinations of this router, and to help troubleshoot the network.

Default Route

A default route is also a static route. A default route is used only when no suitable routing table entry is found. In a routing table, the default route is in the form of the route to the network 0.0.0.0 (with the mask 0.0.0.0). You can determine whether a default route has been set by viewing the output of the display ip routing-tablecommand. If the destination address of a packet fails to match any entry of the routing table, the router selects the default route to forward this packet. If there is no default route and the destination address of the packet fails to match any entry in the routing table, the packet is discarded, and an Internet Control Message Protocol (ICMP) packet is sent to the originating host to indicate that the destination host or network is unreachable.

In a typical network that consists of hundreds of routers, if you used multiple dynamic routing protocols without configuring a default route then significant bandwidth would be consumed. Using the default route can provide appropriate bandwidth, but not high bandwidth, for communications between large numbers of users.

Configuring Static Routes is described in the following sections:

■Configuring Static Routes

■Troubleshooting Static Routes

Static route configuration tasks are described in the following sections:

■Configuring a Static Route

■Configuring a Default Route

■Deleting All Static Routes

■Displaying and Debugging Static Routes

Configuring a Static Route

Perform the following configurations in system view.

Table 79 Configuring a Static Route

Operation	Command
Add a static route	ip route-static ip-address {mask
	mask-length } { interface-name
	gateway-address } [ preference
	value ] [ reject blackhole ]
Delete a static route	undo ip route-static ip-address
	{mask mask-length } {
	interface-name gateway-address}
	[ preference value ]