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148 CHAPTER 6: USING ROUTING PROTOCOL COMMANDS
preference_value Enter the preference level of the route in the range 1 to 255.
The default preference is 60.
reject Enter to indicate an unreachable route.
blackhole Enter to indicate a blackhole route.
Description
Use the ip route-static command to configure a static route.
Use the undo ip route-static command to delete the configured static route.
By default, the system can access the subnet route directly connected to the
router. If you do not use the parameters
preference, reject or blackhole, the
route will be reachable by default with a preference level of 60.
A static route is a special route. You can set up an interconnecting network with a
static route configuration. The problem for such configuration is when a fault
occurs to the network, the static route cannot change automatically to steer away
from the node causing the fault without the help of an administrator.
In a relatively simple network, a system administrator may chose to implement
static routes rather than a dynamic routing protocol. The proper configuration and
usage of static routes can improve the network performance and ensure
bandwidth for important applications.
All the following routes are static routes:
■ Reachable route — A normal route. That is, the IP packet is sent to the next
hop via the route marked by the destination. It is the most 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 will be discarded, and the
originating host will be informed destination unreachable.
■ Blackhole route — If a static route to 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 are
dropped without notifying the source host.
The attributes reject and blackhole are usually used to control the range of
reachable destinations of this router and to help troubleshoot the network.
Use the following precautions when configuring a static route:
■ You cannot specify an interface address of the local Switch as the next hop
address of a static route.
■ When the destination IP address and subnet mask are both set to 0.0.0.0, this
is the configured default route. A packet is forwarded using the default route
as a last resort if no better routing match is found in the routing table.
■ As an alternative way to configure preference level, a flexible routing protocol
can be adopted.
Related command: display ip routing-table, delete static-routes all.