3Com Switch 8800 Configuration Guide Chapter 18 RIP Configuration
18-1
Chapter 18 RIP Configuration

18.1 Introduction to RIP

Routing Information Protocol (RIP) is a relatively simple interior gateway protocol (IGP),
which is mainly applied to small scale networks.
It is easy to implement RIP. You can configure and maintain RIP more easily than OSPF
and IS-IS, so RIP still has a wide application in actual networking.

18.1.1 RIP Operation Mechanism

I. RIP basic concepts
RIP is a kind of Distance-Vector (D-V) algorithm-based protocol and exchanges routing
information via 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 value is an integer ranging
from 0 to 15. The hop count equal to or exceeding 16 is defined as infinite, that is, the
destination network or the host is unreachable.
To improve the performance and avoid route loop, RIP supports Split Horizon and
allows importing the routes discovered by other routing protocols.
II. RIP route database
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:
z Destination address: IP address of a host or a network.
z Next hop address: The interface address of the next router that an IP packet will
pass through for reaching the destination.
z Output interface: The interface through which the IP packet should be forwarded.
z Cost: The cost for the router to reach the destination, which should be an integer in
the range of 0 to 16.
z Timer: 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.
III. RIP timer
In RFC1058, RIP is controlled by the following timers: Period update, Timeout and
Garbage-Collection.