3
Table 1
Dynamic routing protocols
Criterion Categories
Optional scope
•
Interior gateway protocols (IGPs)—Work within an autonomous system (AS).
Examples include RIP, OSPF, and IS-IS.
•
Exterior gateway protocols (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 sharing the same routing policy and working under the same
administration.
•
This chapter focuses on unicast routing protocols. For more information about multicast routing
protocols, see
IP Multicast Configuration Guide.
Routing preference
Different routing protocols can 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. 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.
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
