Advanced SNA/IP : A Simple SNA Transport Protocol
RFC 1538

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Network Working Group                                            W. Behl
Request for Comments: 1538                            McDATA Corporation
Category: Informational                                      B. Sterling
                                                      McDATA Corporation
                                                               W. Teskey
                                                            I/O Concepts
                                                            October 1993

           Advanced SNA/IP : A Simple SNA Transport Protocol

Status of this Memo

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

Abstract

   This RFC provides information for the Internet community about a
   method for establishing and maintaining SNA sessions over an IP
   internet.  While the issues discussed may not be directly relevant to
   the research problems of the Internet, they may be interesting to a
   number of researchers and implementors.  Any questions or comments
   relative to the contents of this RFC may be sent to the following
   Internet address: snaip@mcdata.com.

Table of Contents

   1. Introduction..................................................  2
   2. Motivation and Rationale......................................  2
   3. SNA/IP Protocol Specification.................................  3
   3.1 Glossary.....................................................  3
   3.2 Conventions and Assumptions..................................  3
   3.3 The Protocol.................................................  3
   3.3.1 Connection Establishment...................................  3
   3.3.2 Data Transfer..............................................  5
   3.3.3 Connection Termination and Loss............................  6
   3.3.4 Session Data Flow..........................................  7
   3.3.5 State Transition Table for the Initiating Node.............  8
   4. LLC to SNA/IP Conversion......................................  8
   5. Performance...................................................  8
   6. VTAM Definition...............................................  9
   7. Acknowledgments...............................................  9
   8. References....................................................  9
   9. Security Considerations....................................... 10
   10. Authors' Addresses........................................... 10
   11. Disclaimer................................................... 10

Behl, Sterling & Teskey                                         [Page 1]
RFC 1538                    Advanced SNA/IP                 October 1993

1.  Introduction

   Advanced SNA/IP suggests a method for the transmission of SNA session
   data over an IP network.  This memo documents the SNA/IP protocol as
   implemented in the McDATA LinkMaster(R) 6200 Network Gateway, McDATA
   LinkMaster(R) 7100 Network Controller, and I/O Concepts X-Direct
   TN3270 Server.

   Advanced SNA/IP differs from other protocols designed to enable
   routing of SNA session traffic over an IP network.  SNA/IP was
   originally designed for implementation in peripheral network nodes
   like SNA gateways and downstream nodes (DSNs).  It is the authors'
   view, however, that SNA/IP could also be implemented in intermediate
   network nodes like routers as the base for an LLC to IP subnet
   gateway or data link switch function.

2.  Motivation and Rationale

   The token-ring media access control (MAC) protocol 802.5 and logical
   link control (LLC) protocol 802.2 were the first set of LAN protocols
   used to provide a reliable and connection-oriented data link service
   for SNA sessions in a LAN environment.

   McDATA's experience with transporting SNA over 802.5 networks led to
   an 802.3/802.2 (Ethernet) based variation.  As prospective customers
   were introduced to these Ethernet products, the question of
   routability arose.  Network administrators, accustomed to working
   with Ethernet networks and the IP-based protocols, required an IP
   routable solution.  McDATA's "SNA over Ethernet" products were
   bridgeable, but were not routable.

   SNA sessions require a reliable and connection-oriented data link.
   TCP running over IP provides a reliable and connection-oriented
   transport service and has the added benefit of being routable.  It
   seemed the UDP and TCP protocols could be used in place of 802.2 Type
   I and Type II levels of service used in traditional SNA token-ring
   implementations.  Advanced SNA/IP was created as a result of these
   observations.

Behl, Sterling & Teskey                                         [Page 2]
RFC 1538                    Advanced SNA/IP                 October 1993

3.  SNA/IP Protocol Specification

3.1.  Glossary

   Data Link Switching (DLSw) - This is best described as a routing
   protocol used for the conversion of LLC-based SNA sessions to an IP