HP 6125XLG R2306-HP 6125XLG Blade Switch Layer 3 - IP Routing Configuration Gu - Page 13
Dynamic routing protocols, Route preference
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• Pre-Preference of the route. Among routes to the same destination, the route with the highest preference is optimal. • Cost-If multiple routes to a destination have the same preference, the one with the smallest cost is the optimal route. • NextHop-Next hop. • Interface-Output interface. Dynamic routing protocols Static routes work well in small, stable networks. They are easy to configure and require fewer system resources. However, in networks where topology changes occur frequently, a typical practice is to configure a dynamic routing protocol. Compared with static routing, a dynamic routing protocol is complicated to configure, requires more routers resources, and consumes more network resources. Dynamic routing protocols dynamically collect and report reachability information to adapt to topology changes. They are suitable for large networks. Dynamic routing protocols can be classified by different criteria, as shown in Table 2. Table 2 Categories of dynamic routing protocols Criterion Operation scope Routing algorithm Destination address type IP version Categories • IGPs-Work within an AS. Examples include RIP, OSPF, and IS-IS. • EGPs-Work between ASs. The most popular EGP is BGP. • Distance-vector protocols-Examples include RIP and BGP. BGP is also considered a path-vector protocol. • Link-state protocols-Examples include OSPF and IS-IS. • Unicast routing protocols-Examples include RIP, OSPF, BGP, and IS-IS. • Multicast routing protocols-Examples include PIM-SM and PIM-DM. • IPv4 routing protocols-Examples include RIP, OSPF, BGP, and IS-IS. • IPv6 routing protocols-Examples include RIPng, OSPFv3, IPv6 BGP, and IPv6 IS-IS. An AS refers to a group of routers that use the same routing policy and work under the same administration. Route preference Routing protocols, including static and direct routing, each by default have a preference. If they find multiple routes to the same destination, the router selects the route with the highest preference as the optimal route. The preference of a direct route is always 0 and cannot be changed. You can configure a preference for each static route and each dynamic routing protocol. The following table lists the route types and default preferences. The smaller the value, the higher the preference. Table 3 Route types and default route preferences Route type Direct route Preference 0 2