H3C Technologies H3C S12500 Series Switches - Manual (Page 18)

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• Cost—When multiple routes to a destination have the same preference, the one with the smallest
cost becomes 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 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 based on different criteria, as shown in
Table 2 :
Table 2 Dynamic routing protocols
Criterion Categories
Optional scope
• IGPs—Work within an autonomous system (AS). Examples include RIP, OSPF, and
IS-IS.
• EGPs—Work between ASs. The most popular one is BGP.
Routing algorithm
• Distance-vector protocols—RIP and BGP. BGP is also considered a path-vector
protocol.
• Link-state protocols—OSPF and IS-IS.
Destination address
type
• Unicast routing protocols—RIP, OSPF, BGP, and IS-IS.
• Multicast routing protocols—PIM-SM and PIM-DM.
IP version
• IPv4 routing protocols—RIP, OSPF, BGP, and IS-IS.
• IPv6 routing protocols—RIPng, OSPFv3, IPv6 BGP, and IPv6 IS-IS.
NOTE:
An AS refers to a group of routers that share 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 as required. The following table lists the route types
and default preferences. The smaller the value, the higher the preference.