3Com Switch 7754, Configuration Manual

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32
S
TATIC
R
OUTE
C
ONFIGURATION
Introduction to Static
Route
Static Route Static routes are special routes. They are manually configured by the administrator.
By configuring static routes, you can build an interconnecting network. The
problem for such configuration is when a fault occurs on the network, a static
route cannot change automatically to steer away from the fault point without the
help of the administrator.
In a relatively simple network, you only need to configure static routes to make
routers work normally. Proper configuration and usage of static routes can
improve network performance and ensure sufficient bandwidth for important
applications.
Static routes are divided into three types:
■
Reachable route: normal route. If a static route to a destination is of this type,
the IP packets destined for this destination will be forwarded to the next hop. It
is the most common type of static routes.
■
Unreachable route: route with “” reject ” attribute”. If a static route to a
destination has the “ reject ” attribute, all the IP packets destined for this
destination will be discarded, and the source hosts will be informed of the
unreachability of the destination.
■
Blackhole route: route with “ blackhole ” attribute. If a static route destined for
a destination has the “ blackhole ” attribute, the outgoing interface of this
route is the Null 0 interface regardless of the next hop address, and all the IP
packets addressed to this destination will be dropped without notifying the
source hosts.
The attributes “ reject ” and “ blackhole ” are usually used to limit the range of the
destinations this router can reach, and help troubleshoot the network.
Default Route A default route is a special route. You can manually configure a default route by
using a static route. Some dynamic routing protocols, such as OSPF, can
automatically generate a default route.
Simply put, a default route is a route used only when no matching entry is found
in the routing table. That is, the default route is used only when there is no proper
route. In a routing table, both the destination address and mask of the default
route are 0.0.0.0. You can use the
display ip routing-table command to view
whether the default route has been set. If the destination address of a packet does
not match any entry in the routing table, the router will select the default route for