Chapter 4 Rip Configuration; Rip Overview; Rip Operating Principle - H3C SecPath F1800-A Operation Manual

Operation Manual - Network and Routing Protocol
H3C SecPath F1800-A Firewall

Chapter 4 RIP Configuration

4.1 RIP Overview

Routing Information Protocol (RIP) is a simpler dynamic routing protocol. But it is
widely applied in practice.

4.1.1 RIP Operating Principle

RIP is a kind of Distance-Vector (D-V) algorithm-based protocol and exchanges
routing information through UDP packets. It employs hop count to measure the
distance to the destination host, which is called routing cost. In RIP, the hop count
from a router to its directly connected network is 0, and that to a network which can be
reached through another router is 1, and so on. To restrict the time to converge, RIP
prescribes that the cost is an integer in the range of 0 to 15. The hop count equal to or
more than 16 is defined as infinite, that is to say, the destination network or the host is
unreachable.
RIP sends route refreshment packets every 30 seconds. If the route cannot receive
route refreshment packets from some network neighbor within 180 seconds, it marks
all routes in this network neighbor to be unreachable. If the route can still not receive
route refreshment packets within 300 seconds, it will clear all routes of this network
neighbor from the routing table.
To improve performance and avoid the creation of routing loop, RIP supports both
split horizon and poison reverse. Besides, RIP can also import routes from other
routing protocols.
Each router running RIP manages a route database, which contains routing entries to
all the reachable destinations in the network.
These routing entries contain the following information:
Destination address: refers to the IP address of a host or a network.
Next hop address: refers to the address of the next router that a router will pass
through for reaching the destination.
Interface: refers to the interface through which the IP packet should be
forwarded.
Cost: refers to the cost for the router to reach the destination, which should be an
integer in the range of 0 to 15.
Timer: refers to duration from the last time that the routing entry is modified till
now. The timer is reset to 0 whenever a routing entry is modified.
Route flag: refers to a label to distinguish routes of internal routing protocols from
those of external routing protocols.
5-33
Chapter 4 RIP Configuration