3Com Switch 8800 Configuration Guide Chapter 16 IP Routing Protocol Overview
16-5
Routing protocol or route type The preference of the corresponding
route
UNKNOWN 255
Apart from direct routing, IBGP and EBGP, the preferences of various dynamic routing
protocols can be manually configured to meet the user requirements. In addition, the
preferences for individual static routes can be different.
16.2.2 Supporting Load Sharing and Route Backup I. Load sharing
The Switch 8800 supports static equivalent route, permitting to configure multiple
routes that reach the same destination and use the same precedence. After you
configured static equivalent routes, a packet can reach the same destination through
multiple different paths, whose precedence levels are equal. When there is no route
that can reach the same destination with a higher 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.
The Switch 8800 supports eight routes to implement load sharing.
II. Route backup
The Switch 8800 supports 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.