HP 6125G HP 6125G & 6125G/XG Blade Switches Layer 3 - IP Routing Confi - Page 13

The preference of a direct route is always 0 and cannot be changed. You can manually configure preferences for any other route type. Each static route can be configured with a different preference. The following table lists the types of routes and the default preferences. The smaller the preference value, the higher the preference. Table 3 Route types and their default route preferences Routing approach Direct route OSPF Static route RIP OSPF ASE OSPF NSSA IBGP EBGP Unknown (route from an untrusted source) Preference 0 10 60 100 150 150 255 255 256 Load sharing A routing protocol can be configured with multiple equal-cost routes to the same destination. These routes have the same preference and will all be used to accomplish load sharing if there is no route with a higher preference available. Static routing/IPv6 static routing, RIP/RIPng, OSPF/OSPFv3, and BGP/IPv6 BGP supports ECMP load sharing. Route backup Route backup can improve network availability. Among multiple routes to the same destination, the route with the highest preference is the main route and all others are backup routes. The router forwards matching packets through the main route. When the main route fails, the route with the highest preference among the backup routes is selected to forward packets. When the main route recovers, the router uses it to forward packets. Route recursion To use a BGP route, static route (that is configured with a next hop but with no output interface), or RIP route that has an indirectly-connected next hop, a router must perform route recursion to find the outgoing interface to reach the next hop. Link-state routing protocols, such as OSPF, do not need route recursion, because they obtain directly-connected next hops through route calculation. 3