3Com SuperStack 4 Configuration Manual page 102

114 C 6: IP R
HAPTER OUTING
P O
ROTOCOL PERATION
Table 107 Routing Protocols and the Default Preferences for Routes
Routing protocol or route type
IBGP
EBGP
UNKNOWN
In Table 107, 0 indicates a direct route, and 255 indicates any route from an
unreliable source.
Except for direct routing and BGP (IBGP and EBGP), the preferences of various
dynamic routing protocols can be manually configured to meet the user
requirements. The preferences for individual static routes can be different.
Supporting Load Sharing and Route Backup
I. Load sharing
Supports multi-route mode, allowing the user to configure multiple routes that
reach the same destination and use the same precedence. The same destination
can be reached via multiple different paths, whose precedences are equal. When
there is no route that can reach the same destination with a higher precedence,
the multiple routes will be adopted by IP, which will forward the packets to the
destination via these paths so as to implement load sharing.
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 5500G-EI supports three routes to implement load sharing.
II. Route backup
Supports route backup. If the main route is in failure, the unit will automatically
switch to a backup route to improve the network reliability.
To achieve route backup, the user can configure multiple routes to the same
destination according to actual situation. One of the routes has the highest
precedence and is called the main route. The other routes have descending
precedences and are called backup routes. Normally, the router sends data via the
main route. When the line fails, the main route will hide itself and the router will
choose from one of the remaining routes as a backup route whose precedence is
higher than the others to send data. This process is the switchover from the main
route to the backup route. When the main route recovers, the router will restore it
by re-selecting the main route. As the main route has the highest precedence, the
router will select the main route again to send data. This process is the automatic
switchover from the backup route to the main route.
Routes Shared between Routing Protocols
As the algorithms of various routing protocols are different, different protocols can
generate different routes. This situation creates the problem of how to resolve the
different routes being generated by different routing protocols. The Switch
5500G-EI can import the information of another routing protocol. Each protocol
has its own route redistribution mechanism. For details, refer to
The preference of the corresponding route
256
256
255
"Enabling RIP to