Proposed standard for the transmission of IP datagrams over FDDI Networks
RFC 1103

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Network Working Group                                            D. Katz
Request for Comments:  1103                                 Merit/NSFNET
                                                               June 1989

              A Proposed Standard for the Transmission of
                    IP Datagrams over FDDI Networks

Status of this Memo

   This RFC specifies a method of encapsulating the Internet Protocol
   (IP) [1] datagrams and Address Resolution Protocol (ARP) [2] requests
   and replies on Fiber Distributed Data Interface (FDDI) Networks.
   This RFC specifies a proposed protocol standard for the Internet
   community.  Comments are welcome.  Distribution of this memo is
   unlimited.

Acknowledgment

   This memo draws heavily in both concept and text from RFC 1042 [3],
   written by Jon Postel and Joyce K. Reynolds of USC/Information
   Sciences Institute.

Conventions

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

      "Must" 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 implementor.

Introduction

   The goal of this specification is to allow compatible and
   interoperable implementations for transmitting IP datagrams and ARP
   requests and replies.

   The Fiber Distributed Data Interface (FDDI) specifications define a
   family of standards for Local Area Networks (LANs) that provides the
   Physical Layer and Media Access Control Sublayer of the Data Link
   Layer as defined by the ISO Open System Interconnection Reference
   Model (ISO/OSI).  Documents are in various stages of progression

Katz                                                            [Page 1]
RFC 1103            IP Datagrams over FDDI Networks            June 1989

   toward International Standardization for Media Access Control (MAC)
   [4], Physical Layer Protocol (PHY) [5], Physical Layer Medium
   Dependent (PMD) [6], and Station Management (SMT) [7].  The family of
   FDDI standards corresponds to the IEEE 802 MAC layer standards [8, 9,
   10].

   The remainder of the Data Link Service is provided by the IEEE 802.2
   Logical Link Control (LLC) service [11].  The resulting stack of
   services appears as follows:

           +-------------+
           |   IP/ARP    |
           +-------------+
           |  802.2 LLC  |
           +-------------+
           |  FDDI MAC   |
           +-------------+
           |  FDDI PHY   |
           +-------------+
           |  FDDI PMD   |
           +-------------+

   This memo describes the use of IP and ARP in this environment.  At
   this time, it is not necessary that the use of IP and ARP be
   consistent between FDDI and IEEE 802 networks, but it is the intent
   of this memo not to preclude Data Link Layer interoperability at such
   time as the standards define it.

Packet Format

   IP datagrams and ARP requests and replies sent on FDDI networks must
   be encapsulated within the 802.2 LLC and Sub-Network Access Protocol
   (SNAP) data link layers and the FDDI MAC and physical layers.  The
   SNAP must be used with an Organization Code indicating that the SNAP
   header contains the EtherType code (as listed in Assigned Numbers
   [12]).

   802.2 LLC Type 1 communication (which must be implemented by all
   conforming 802.2 stations) is used exclusively.  All frames must be
   transmitted in standard 802.2 LLC Type 1 Unnumbered Information
   format, with the DSAP and the SSAP fields of the 802.2 header set to
   the assigned global SAP value for SNAP [11].  The 24-bit Organization
   Code in the SNAP must be zero, and the remaining 16 bits are the
   EtherType from Assigned Numbers [12] (IP = 2048, ARP = 2054).

Katz                                                            [Page 2]
RFC 1103            IP Datagrams over FDDI Networks            June 1989

     ...--------+--------+--------+
                MAC Header        |                           FDDI MAC
     ...--------+--------+--------+

     +--------+--------+--------+
     | DSAP=K1| SSAP=K1| Control|                            802.2 LLC
     +--------+--------+--------+

     +--------+--------+---------+--------+--------+
     |Protocol Id or Org Code =K2|    EtherType    |        802.2 SNAP
     +--------+--------+---------+--------+--------+

     The total length of the LLC Header and the SNAP header is 8
     octets.

     The K1 value is 170 (decimal).

     The K2 value is 0 (zero).

     The control value is 3 (Unnumbered Information).

Address Resolution

   The mapping of 32-bit Internet addresses to 16-bit or 48-bit FDDI
   addresses must be done via the dynamic discovery procedure of the
   Address Resolution Protocol (ARP) [2].

   Internet addresses are assigned arbitrarily on Internet networks.