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Static Routes 85
■ 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-table
command. 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
Configuring 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 ]