3Com 5500 SI - Switch - Stackable, Configuration Manual

Page: 221 / 686

Static Routes 221
The following routes are static routes:
■
Reachable route—The IP packet is sent to the next hop towards the destination.
This is a common type of static route.
■
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—If 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 for the router, and to help troubleshoot the network.
Default Route
The default route is also a static route. The 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 is
consumed. Using the default route can provide appropriate bandwidth for
communications between large numbers of users.
Static Routes configuration 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 The Static Routes
■
Displaying and Debugging Static Routes
Configuring a Static Route
Perform the following configurations in System View.
Table 198 Configuring a static route
Operation Command
Add a static route
ip route-static ip_address { mask | mask_length } {
interface_type interface_number | gateway_address } [
preference value ] [ reject | blackhole ]
Delete a static
route
undo ip route-static ip_address { mask | mask_length }
[ interface_type interface_number | gateway_address ] [
preference value ] [ reject | blackhole ]