RFC1132

Network Working Group L. McLaughlin III Request for Comments: 1132 The Wollongong Group

                                                          November 1989

  A Standard for the Transmission of 802.2 Packets over IPX Networks

Status of this Memo

  This document specifies a standard method of encapsulating 802.2 [1]
  packets on networks supporting Novell's Internet Packet Exchange
  Protocol [2] (IPX).  It obsoletes earlier documents detailing the
  transmission of Internet packets over IPX networks.  It differs from
  these earlier documents in that it allows for the transmission of
  multiple network protocols over IPX and for the transmission of
  packets through IPX bridges.  Distribution of this memo is unlimited.

Introduction

  The goal of this specification is to allow compatible and
  interoperable implementations for transmitting Internet packets such
  as the Internet Protocol [3] (IP) and Address Resolution Protocol [4]
  (ARP) as well as the Connectionless-mode Network Protocol [5] (CLNP)
  over IPX networks.

  IPX is a proprietary standard developed by Novell derived from
  Xerox's Internet Datagram Protocol [6] (IDP). Defining the
  encapsulation of the IEEE 802.2 Data Link Layer Standard over IPX in
  terms of yet another 802.X Physical Layer standard allows for the
  transmission of IP Datagrams as described in RFC 1042 [7].  This
  document will focus on the implementation of that RFC over IPX
  networks.

Description

  In general, this specification allows IPX networks to be used to
  support any network protocol which can use the IEEE 802.2 Data Link
  Layer specification.

  More specifically, IPX networks may be used to support IP networks
  and subnetworks of any class.  By encapsulating IP datagrams within
  IPX datagrams and assigning IP numbers to the hosts on a IPX network,
  IP-based applications are supported on these hosts.  The addition of
  an IP Gateway capable of encapsulating IP packets within 802.IPX
  datagrams would allow those hosts on an IPX network to communicate
  with the Internet.

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RFC 1132 802.2 Packets over IPX Networks November 1989

Maximum Transmission Unit

  The maximum data size of a IPX datagram is 546 bytes.  As the
  combined size of the 802.2 LLC and SNAP headers is 8 bytes, this
  results in a Maximum Transmission Unit (MTU) of 538 bytes.

Address Mappings

  The mapping of Internet Protocol addresses to 802.IPX addresses is
  done using the Address Resolution Protocol in the same fashion as
  with other IEEE 802.X physical addresses.  However, the length of an
  802.IPX physical address is 10 bytes rather than 2 or 6.  This 10
  byte physical address consists of the 4 bytes of the IPX network
  address followed by the 6 bytes of the IPX node address.

Byte Order

  The byte transmission order is "big-endian" [8].

Broadcast Addresses

  IPX packets may be broadcast by setting the IPX header Packet Type
  field to 0x14, the Destination Network field to the local network
  number, the the Destination Node field to 0xffffff, and the Immediate
  Address field of the IPX Event Control Block to 0xffffff.

Unicast Addresses

  IPX packets may be unicast by setting the IPX header Packet Type
  field to 0x04, the Destination Network field and Destination Node
  field to those values found by address resolution, and the Immediate
  Address field of the IPX Event Control Block to the physical address
  of the destination node or the appropriate IPX bridge.

Checksum

  Like most IPX applications, this specification does not use IPX
  checksum.

Reserved values

  The IPX socket 0x8060 has been reserved by Novell for the
  implementation of this protocol.

Implementation

  The encapsulation of Internet packets within IPX networks has proved
  to be quite useful.  Because the IPX interface insulates knowledge of

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RFC 1132 802.2 Packets over IPX Networks November 1989

  the physical layer from an application, 802.2 over IPX networks work
  over any physical medium.  A typical IP over IPX packet is shown
  below:

                             --------------------
                   N bytes   |  physical header |
                             |------------------|
                  30 bytes   |    IPX header    |
                             |------------------|
                   8 bytes   |   802.2 header   |
                             |------------------|
          usually 20 bytes   |     IP header    |
                             |------------------|
          usually 20 bytes   |    TCP header    |
                             |------------------|
           up to 498 bytes   |    TCP data      |
                             --------------------

  On workstations supporting an IPX programming interface,
  implementation of this specification has proved fairly
  straightforward.  The only change which was done was to modify the
  existing address resolution protocol code to allow for cache entries
  larger than the hardware address length.  This was done to allow room
  for the immediate address of a possible intervening IPX bridge in
  addition to the destination node and network addresses to be
  associated with a given IP address.

  Thus far, no implementations have been attempted on systems which do
  not already support an IPX programming interface (e.g., a dedicated
  router) though a few implementation details can be noted.  First,
  obviously any such implementation will have to distinguish IPX
  packets from other packets; this process will be media dependent.
  Second, note that no unicast packet is ever sent from host1 to host2
  without a prior broadcast packet from host2 to host1.  Thus, the
  immediate address of a possible intervening IPX bridge between host1
  and host2 can be learned from the physical header of that prior
  broadcast packet.  Third, any such implementation will need to
  discover the local IPX network number from a Novell bridge or file
  server.  The mechanisms for doing this exist but documentation for
  their use is not commonly available.

References

 [1]  IEEE, "IEEE Standards for Local Area Networks: Logical Link
      Control", IEEE, New York, 1985.

 [2]  Novell, Inc., "Advanced NetWare V2.1 Internetwork Packet Exchange
      Protocol (IPX) with Asynchronous Event Scheduler (AES)", October

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RFC 1132 802.2 Packets over IPX Networks November 1989

      1986.

 [3]  Postel, J., "Internet Protocol", RFC-791, USC/Information
      Sciences Institute, September 1981.

 [4]  Plummer, D., "An Ethernet Address Resolution Protocol", RFC-826,
      November 1982.

 [5]  ISO DIS 8473: "Information Processing Systems - Data
      Communications - Protocol for Providing the Connectionless-mode
      Network Service".

 [6]  Xerox Corporation, "Xerox Network Systems Architecture", XNSG
      068504, April 1985.

 [7]  Postel, J., and J. Reynolds, "A Standard for the Transmission of
      IP Datagrams over IEEE 802 Networks", RFC-1042, USC/Information
      Sciences Institute, February 1988.

 [8]  Cohen, D., "On Holy Wars and a Plea for Peace", Computer, IEEE,
      October 1981.

Security Considerations

  Security issues are not addressed in this memo.

Author's Address:

  Leo J. McLaughlin III
  The Wollongong Group
  1129 San Antonio Road
  Palo Alto, CA 94303

  Phone: (415) 962-7100

  EMail: [email protected]

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