1-4Routing Protocols and Routing PriorityDifferent 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 canuniquely 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 routingprotocol 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 routeRouting approach PriorityDIRECT 0OSPF 10STATIC 60RIP 100OSPF ASE 150OSPF NSSA 150UNKNOWN 255z 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 canhave their priorities manually configured.z Each static route can be configured with a different priority.Load Sharing and Route BackupLoad sharingA given routing protocol may find several routes with the same metric to the same destination, and if thisprotocol has the highest priority among all the active protocols, these routes will be considered valid andare used to forward packets, thus achieving load sharing.Route backupYou can configure multiple routes to the same destination, expecting the one with the highest priority tobe the primary route and all the rest backup routes.Route backup can help improve network reliability. Automatic switching can happen between theprimary route and a backup route.
