H3C Technologies H3C S3600 Series Switches - Manual (Page 310)

1-4
Routing Protocols and Routing Priority
Different routing protocols may find different routes (including static routes) to the same destination.
However, not all of those routes are optimal. In fact, at a particular moment, only one protocol can
uniquely determine the current optimal routing to the destination. For the purpose of route selection,
each routing protocol (including static routes) is assigned a priority. The route found by the routing
protocol with the highest priority is preferred.
The following table lists some routing protocols and the default priorities for routes found by them:
Table 1-1 Routing protocols and priorities of their default route
Routing approach Priority
DIRECT 0
OSPF 10
STATIC 60
RIP 100
OSPF ASE 150
OSPF NSSA 150
UNKNOWN 255
z The smaller the priority value, the higher the priority.
z The priority for a direct route is always 0, which you cannot change. Any other type of routes can
have their priorities manually configured.
z Each static route can be configured with a different priority.
Load Sharing and Route Backup
Load sharing
A given routing protocol may find several routes with the same metric to the same destination, and if this
protocol has the highest priority among all the active protocols, these routes will be considered valid and
are used to forward packets, thus achieving load sharing.
Route backup
You can configure multiple routes to the same destination, expecting the one with the highest priority to
be the primary route and all the rest backup routes.
Route backup can help improve network reliability. Automatic switching can happen between the
primary route and a backup route.
Under normal circumstances, packets are forwarded through the primary route. When the primary route
goes down, the route with the highest priority among the backup routes is selected to forward packets.
When the primary route recovers, the route selection process is performed again and the primary route
is selected again to forward packets.