3Com 8807 Configuration Manual page 283

Routing Management Policy 283
precedence, the multiple routes will be adopted. Thus, the router will forward the
packets to the destination through these paths according to a certain algorithm so
as to implement load sharing.
For the same destination, a specified routing protocol may find multiple different
routes with the same precedence and different next hops. 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.
By far, Switch 8800 Family series support eight routes to implement load sharing.
Route backup
The Switch 8800 Family series support route backup. When the main route fails,
the system will automatically switch to a backup route to improve the network
reliability.
In order to achieve static route backup, the user can configure multiple routes to
the same destination according to actual situations. One of the routes has the
highest precedence and is called as main route. The other routes have descending
precedence levels and are called as backup routes. Normally, the router sends data
via main route. When the line fails, the main route will hide itself and the router
will choose one from the left routes as a backup route whose precedence is higher
than others' to send data. In this way, the switchover from the main route to the
backup route is implemented. When the main route recovers, the router will
restore it and re-select route. As the main route has the highest precedence, the
router still chooses the main route to send data. This process is the automatic
switchover from the backup route to the main route.
Routes Shared Between As the algorithms of various routing protocols are different, different protocols
Routing Protocols may generate different routes, thus bringing about the problem of how to resolve
the differences when different routes are generated by different routing protocols.
The Switch 8800 Family series support the import of routes discovered by one
routing protocol into another. Each protocol has its own route importing
mechanism. For details, refer to the description about "Importing an External
Route" in the operation manual of the corresponding routing protocol.