Use of ISO CLNP in TUBA Environments
RFC 1561

Document Type RFC - Experimental (December 1993; No errata)
Author David Piscitello 
Last updated 2013-03-02
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Network Working Group                                      D. Piscitello
Request for Comments: 1561                               Core Competence
Category: Experimental                                     December 1993

                  Use of ISO CLNP in TUBA Environments

Status of this Memo

   This memo defines an Experimental Protocol for the Internet
   community.  This memo does not specify an Internet standard of any
   kind.  Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.


   This memo specifies a profile of the ISO/IEC 8473 Connectionless-mode
   Network Layer Protocol (CLNP, [1]) for use in conjunction with RFC
   1347, TCP/UDP over Bigger Addresses (TUBA, [2]).  It describes the
   use of CLNP to provide the lower-level service expected by
   Transmission Control Protocol (TCP, [3]) and User Datagram Protocol
   (UDP, [4]).  CLNP provides essentially the same datagram service as
   Internet Protocol (IP, [5]), but offers a means of conveying bigger
   network addresses (with additional structure, to aid routing).

   While the protocols offer nearly the same services, IP and CLNP are
   not identical. This document describes a means of preserving the
   semantics of IP information that is absent from CLNP while preserving
   consistency between the use of CLNP in Internet and OSI environments.
   This maximizes the use of already-deployed CLNP implementations.


   Many thanks to Ross Callon (Wellfleet Communications), John Curran
   (BBN), Cyndi Jung (3Com), Paul Brooks (UNSW), Brian Carpenter (CERN),
   Keith Sklower (Cal Berkeley), Dino Farinacci and Dave Katz (Cisco
   Systems), Rich Colella (NIST/CSL) and David Oran (DEC) for their
   assistance in composing this text.

Piscitello                                                      [Page 1]
RFC 1561               CLNP in TUBA Environments           December 1993


   The following language conventions are used in the items of
   specification in this document:

         * MUST, SHALL, or MANDATORY -- the item is an absolute
           requirement of the specification.

         * SHOULD or RECOMMENDED -- the item should generally be
           followed for all but exceptional circumstances.

         * MAY or OPTIONAL -- the item is truly optional and may be
           followed or ignored according to the needs of the

1.  Terminology

   To the extent possible, this document is written in the language of
   the Internet. For example, packet is used rather than "protocol data
   unit", and "fragment" is used rather than "segment".  There are some
   terms that carry over from OSI; these are, for the most part, used so
   that cross-reference between this document and RFC 994 [6] or ISO/IEC
   8473 is not entirely painful.  OSI acronyms are for the most part

2.  Introduction

   The goal of this specification is to allow compatible and
   interoperable implementations to encapsulate TCP and UDP packets in
   CLNP data units. In a sense, it is more of a "hosts requirements"
   document for the network layer of TUBA implementations than a
   protocol specification. It is assumed that readers are familiar with
   STD 5, RFC 791, STD 5, RFC 792 [7], STD 3, RFC 1122 [8], and, to a
   lesser extent, RFC 994 and ISO/IEC 8473.  This document is compatible
   with (although more restrictive than) ISO/IEC 8473; specifically, the
   order, semantics, and processing of CLNP header fields is consistent
   between this and ISO/IEC 8473.

   [Note: RFC 994 contains the Draft International Standard version of
   ISO CLNP, in ASCII text. This is not the final version of the ISO/IEC
   protocol specification; however, it should provide sufficient
   background for the purpose of understanding the relationship of CLNP
   to IP, and the means whereby IP information is to be encoded in CLNP
   header fields. Postscript versions of ISO CLNP and associated routing
   protocols are available via anonymous FTP from, and may be
   found in the directory /pub/ISO/IEC.

Piscitello                                                      [Page 2]
RFC 1561               CLNP in TUBA Environments           December 1993

3.  Overview of CLNP

   ISO CLNP is a datagram network protocol. It provides fundamentally
   the same underlying service to a transport layer as IP. CLNP provides
   essentially the same maximum datagram size, and for those
   circumstances where datagrams may need to traverse a network whose
   maximum packet size is smaller than the size of the datagram, CLNP
   provides mechanisms for fragmentation (data unit identification,
   fragment/total length and offset). Like IP, a checksum computed on
   the CLNP header provides a verification that the information used in
   processing the CLNP datagram has been transmitted correctly, and a
   lifetime control mechanism ("Time to Live") imposes a limit on the
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