Discussion

By default, the JUNOS software implements both split horizon and poison reverse.
For service provider networks that use Juniper Networks routers, IS-IS or OSPF are
generally used for the IGP because they are more powerful routing protocols and
have more features for the larger service provider networks. You might have to use
RIP for part of your network if it still has devices running RIP or for one of your customers
if they still have devices running RIP. You might choose to use RIP because it
is a relatively simple protocol, has very few advanced features, and is relatively
straightforward to configure and manage. RIP can be useful in a small, reasonably
homogeneous network, which might be served by some of the newer, smaller J-series
routers.
This chapter discusses how to enable RIP on the router, how to set it up to receive
and send both Version 1 and Version 2 protocol update packets, how to set up some
simple routing policies to filter the traffic that RIP sends and receives, and how to
perform basic troubleshooting of RIP traffic.
If you use RIP, you should remember that the protocol itself has some inherent limitations.
RIP can be used only in small networks because the maximum number of
hops to a destination is 16. If a RIP device is more than 15 hops away, it is considered
to be unreachable. In practice, this is often a serious limitation. From a route
convergence point of view, you should use RIP only if your network is small, with no
devices more than four hops from each other. If the network diameter is larger than
this, the route convergence time increases to about two to four minutes, which can
lead to network instabilities and routers becoming unreachable. In comparison,
OSPF and IS-IS typically converge in about 40 seconds. Although it is possible to
influence the convergence times by altering RIP timers, if you find yourself having to
do this, you should consider using OSPF or IS-IS instead of RIP.
RIP Version 1 has two additional limitations. First, it uses only classful routing, so it
cannot handle subnet and network mask information. Second, it uses clear-text password
authentication, which is vulnerable to attack. RIP Version 2 was developed to
address these two limitations, supporting CIDR and MD5 authentication. However,
the hop-count limit of 15 was retained to maintain interoperability with Version 1.
The JUNOS implementation of RIP also has a design point of note. By default, the
JUNOS RIP only listens to RIP updates. The router does not send RIP updates unless
you explicitly tell RIP to do so. You do this by creating a routing policy, which can
be a fairly simple policy, to advertise the routes.
10.1 Configuring RIP
Problem
You want network devices running RIP Version 2 to be able to communicate with
the rest of your network.
This is the Title of the Book, eMatter Edition
Copyright © 2008 O’Reilly & Associates, Inc. All rights reserved.
Configuring RIP | 333