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Network Working Group                                  L. McLaughlin IIIRequest for Comments: 1132                          The Wollongong Group                                                           November 1989A Standard for the Transmission of 802.2 Packets over IPX NetworksStatus 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 inRFC 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.McLaughlin                                                      [Page 1]

RFC 1132            802.2 Packets over IPX Networks        November 1989Maximum 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 ofMcLaughlin                                                      [Page 2]

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)", OctoberMcLaughlin                                                      [Page 3]

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: ljm@TWG.COMMcLaughlin                                                      [Page 4]