RFC1721 - RIP Version 2 Protocol Analysis

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　　Network Working Group G. Malkin
Request for Comments: 1721 Xylogics, Inc.
Obsoletes: 1387 November 1994
Category: Informational

RIP Version 2 Protocol Analysis

Status of this Memo

This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. Distribution of
this memo is unlimited.

Abstract

As required by Routing Protocol Criteria (RFC1264), this report
documents the key features of the RIP-2 protocol and the current
implementation experience. This report is a prerequisite to
advancing RIP-2 on the standards track.

Acknowledgements

The RIP-2 protocol owes much to those who participated in the RIP-2
working group. A special thanks goes to Fred Baker, for his help on
the MIB, and to Jeffrey Honig, for all his comments.

1. Protocol Documents

The RIP-2 applicability statement is defined in RFC1722 [1].

The RIP-2 protocol description is defined in RFC1723 [2]. This memo
obsoletes RFC1388, which specifies an update to the "Routing
Information Protocol" RFC1058 (STD 34).

The RIP-2 MIB description is defined in RFC1724 [3]. This memo
obsoletes RFC1389.

2. Key Features

While RIP-2 shares the same basic algorithms as RIP-1, it supports
several new features. They are: external route tags, subnet masks,
next hop addresses, and authentication.

The significant change from RFC1388 is the removal of the domain
field. There was no clear agreement as to how the field would be
used, so it was determined to leave the field reserved for future
expansion.

2.1 External Route Tags

The route tag field may be used to propagate information acquired
from an EGP. The definition of the contents of this field are beyond
the scope of this protocol. However, it may be used, for example, to
propagate an EGP AS number.

2.2 Subnet Masks

Inclusion of subnet masks was the original intent of opening the RIP
protocol for improvement. Subnet mask information makes RIP more
useful in a variety of environments and allows the use of variable
subnet masks on the network. Subnet masks are also necessary for
implementation of "classless" addressing, as the CIDR work proposes.

2.3 Next Hop Addresses

Support for next hop addresses allows for optimization of routes in
an environment which uses multiple routing protocols. For example,
if RIP-2 were being run on a network along with another IGP, and one
router ran both protocols, then that router could indicate to the
other RIP-2 routers that a better next hop than itself exists for a
given destination.

2.4 Authentication

One significant improvement RIP-2 offers over RIP-1, is the addition
of an authentication mechanism. Essentially, it is the same
extensible mechanism provided by OSPF. Currently, only a plain-text
password is defined for authentication. However, more sophisticated
authentication schemes can easily be incorporated as they are
defined.

2.5 Multicasting

RIP-2 packets may be multicast instead of being broadcast. The use
of an IP multicast address reduces the load on hosts which do not
support routing protocols. It also allows RIP-2 routers to share
information which RIP-1 routers cannot hear. This is useful since a
RIP-1 router may misinterpret route information because it cannot
apply the supplied subnet mask.

3. RIP-2 MIB

The MIB for RIP-2 allows for monitoring and control of RIP's
operation within the router. In addition to global and per-interface
counters and controls, there are per-peer counters which provide the
status of RIP-2 "neighbors".

The MIB was modified to deprecate the domain, which was removed from
the protocol. It has also been converted into version 2 format.

4. Implementations

Currently, there are three complete implementations of RIP-2: GATED,
written by Jeffrey Honig at Cornell University; Xylogics's Annex
Communication server; and an implementation for NOS, written by Jeff
White. The GATED implementation is available by anonymous FTP from
gated.cornell.edu as pub/gated/gated-alpha.tar.Z. The implementation
for NOS is available by anonymous FTP from ucsd.edu as
/hamradio/packet/tcpip/incoming/rip2.zip.

Additionally, Midnight Networks has produced a test suite which
verifies an implementation's conformance to RFC1388 implemented over
RFC1058.

The author has conducted interoperability testing between the GATED
and Xylogics implementations and found no incompatibilities. This
testing includes verification of protection provided by the
authentication mechanism described in section 2.4.

5. Operational experience

Xylogics has been running RIP-2 on its production systems for five
months. The topology includes seven subnets in a class B address and
various, unregistered class C addresses used for dial-up access. Six
systems, in conjunction with three routers from other vendors and
dozens of host systems, operate on those subnets.

The only problem which has appeared is the reaction of some routers
to Version 2 RIP packets. Contrary to RFC1058, these routers
discard Version 2 packets rather than ignoring the fields not defined
for Version 1.

6. References

[1] Malkin, G., "RIP Version 2 Protocol Applicability Statement", RFC
1722, Xylogics, Inc., November 1994.

[2] Malkin, G., "RIP Version 2 - Carrying Additional Information",
RFC1723, Xylogics, Inc., November 1994.

[3] Malkin, G., and F. Baker, "RIP Version 2 MIB Extension", RFC
1724, Xylogics, Inc., Cisco Systems, November 1994.

7. Security Considerations

Security issues are discussed in sections 2.4 and 4.

8. Author's Address

Gary Scott Malkin
Xylogics, Inc.
53 Third Avenue
Burlington, MA 01803

Phone: (617) 272-8140
EMail: gmalkin@Xylogics.COM

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