H3C Technologies H3C SecBlade NetStream Cards - Manual (Page 87)

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Criterion Categories
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.
• This chapter focuses on unicast routing protocols.
Routing preference
Different routing protocols may find different routes to the same destination. However, not all of those
routes are optimal. For route selection, routing protocols, direct routes, and static routes are assigned
different preferences. The route with the highest preference is preferred.
The preference of a direct route is always 0 and cannot be changed. All other types of routes can have
their preferences manually configured. 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.
Routing approach Preference
Direct route 0
OSPF 10
IS-IS 15
Static route 60
RIP 100
OSPF ASE 150
OSPF NSSA 150
IBGP 255
EBGP 255
Unknown (route from an untrusted source) 256
Route recursion
The next hops of some BGP routes (except eBGP routes) and static routes configured with next hops may
not be directly connected. The outgoing interface to reach the next hop must be available. Route
recursion is used to find the outgoing interface based on the next hop information of the route. Link-state
routing protocols, such as OSPF and IS-IS, do not need route recursion because they obtain next hop
information through route calculation.