3com 3.01.01 User Manual

main route. When the line fails, the main route hides itself and the router chooses 
one from the remaining routes as a backup route whose precedence is higher than 
others' to send data. When the main route recovers, the router restores it and 
re-selects a route. As the main route has the highest precedence, the router 
chooses the main route to send data. This process is the automatic switchover 
from the backup route to the main route. 

For the same destination, a specified routing protocol may find multiple different 
routes. If the routing protocol has the highest precedence among all active routing 
protocols, these multiple routes will be regarded as currently valid routes. Thus, 
load sharing of IP traffic is ensured in terms of routing protocols. The Switch 8800 
supports four routes to implement load sharing. 

As the algorithms of various routing protocols are different, different protocols can 
generate different routes. This situation creates the problem of how to resolve 
different routes being generated by different routing protocols. The Switch 8800 
supports an operation to import the routes generated by one routing protocol into 
another routing protocol. Each protocol has its own route redistribution 
mechanism. For details, refer to “Enabling RIP to Import Routes of Other 
Protocols”, “Configuring OSPF to Import the Routes of Other Protocols”, or 
“Importing Routing Information Discovered by Other Routing Protocols”. 

A static route is a route that is manually configured by the network administrator. 
You can set up an interconnected network using static routes. However, if a fault 
occurs in the network, the static route cannot change automatically to steer 
packets away from the fault without the help of the administrator.

In a relatively simple network, you only need to configure static routes to make the 
router work normally. The proper configuration and usage of the static route can 
improve network performance and ensure bandwidth for important applications.

The following routes are static routes:

■

Reachable route — The normal route in which the IP packet is sent to the next 
hop towards the destination. It 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 — 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.

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