Routing Protocols And Routing Priority - H3C S5500-EI series Operation Manual

Operation Manual – IP Routing-GR Overview
H3C S5500-EI Series Ethernet Switches
I. Operational scope
Interior gateway protocols (IGPs): Work within an autonomous system, including
RIP, OSPF, and IS-IS.
Exterior gateway protocols (EGPs): Work between autonomous systems. The
most popular one is BGP.
Note:
An autonomous system refers to a group of routers that share the same routing policy
and work under the same administration.
II. Routing algorithm
Distance-vector protocols: RIP and BGP. BGP is also considered a path-vector
protocol.
Link-state protocols: OSPF and IS-IS.
The main differences between the above two types of routing algorithms lie in the way
routes are discovered and calculated.
III. Type of the destination address
Unicast routing protocols: RIP, OSPF, BGP, and IS-IS.
Multicast routing protocols: PIM-SM and PIM-DM.
This chapter focuses on unicast routing protocols. For information on multicast routing
protocols, refer to the Multicast Protocol Configuration.
IV. Version of IP protocol
IPv4 routing protocols: RIP, OSPFv2, BGP4 and IS-IS.
IPv6 routing protocols: RIPng, OSPFv3, IPv6 BGP, and IPv6 IS-IS.

1.2.3 Routing Protocols and Routing Priority

Different routing protocols may find different routes to the same destination. However,
not all of those routes are optimal. In fact, at a particular moment, only one protocol can
uniquely determine the current optimal routing to the destination. For the purpose of
route selection, each routing protocol (including static routes) is assigned a priority. The
route found by the routing protocol with the highest priority is preferred.
1-4
Chapter 1 IP Routing Overview