Discussion

Chapter
CHAPTER
10
10
RIP 10
10.0 Introduction
The Routing Information Protocol (RIP) is an interior gateway protocol (IGP) that
was developed as part of the ARPANET project and was included in the Unix BSD
operating system in the early 1980s. RIP was widely deployed in the 1980s and
became the industry standard for interior routing. It was standardized by the IETF in
1988, in RFC 1058. This version is referred to as RIP Version 1. RIP Version 2,
defined in RFC 2453, added support for Classless Interdomain Routing (CIDR) and
authentication. RIP Version 2 MD5 authentication is defined in RFC 2082. RFCs
2080 and 2081 define RIPng, which is designed for IPv6 networks. JUNOS software
supports RIP Versions 1 and 2, and RIPng.
RIP is a relatively simple protocol. It uses a distance-vector algorithm (also called the
Bellman-Ford algorithm) to determine the best route to a destination. The distance is
measured in hops, which is the number of routers that a packet must pass through to
reach the destination. The best route is the one with the shortest number of hops. In
the routing table, the router maintains two basic pieces of information for RIP
routes: the IP address of the destination network or host and the hop count (metric)
to that destination.
Every 30 seconds, devices on a RIP network broadcast RIP route information, which
describes their view of the network topology and generates a lot of traffic on the network.
RIP uses two techniques to reduce the amount of traffic:
Split horizon
A device receives a route advertisement on an interface but does not retransmit
that advertisement back on the same interface. This limits the amount of RIP
traffic by eliminating information that its RIP neighbor has already learned.
Poison reverse
If a RIP device learns from an interface that a device is no longer connected or
reachable, it advertises that device’s route back on the same interface, setting the
number of hops to 16, which means infinite or unreachable. Poison reverse
improves the convergence time on a RIP network.
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