RFC 1234 (rfc1234) - Page 2 of 6

Tunneling IPX traffic through IP networks

RFC 1234                       IPX on IP                       June 1991


   +---------------------+------------+-------------------------------+
   |                     |            |             |                 |
   |     IP Header       | UDP Header | IPX Header  | IPX packet data |
   | (20 or more octets) | (8 octets) | (30 octets) |                 |
   |                     |            |             |                 |
   +---------------------+------------+-------------------------------+

         Figure 1: An IPX packet carried as data in a UDP packet.

Reserved Packets

   The first two octets of the IPX header contain the IPX checksum.  IPX
   packets are never sent with a checksum, so every IPX header begins
   with two octets of FF hex.  Implementations of this encapsulation
   scheme should ignore packets with any other value in the first two
   octets immediately following the UDP header.  Other values are
   reserved for possible future enhancements to this encapsulation
   protocol.

Unicast Address Mappings

   IPX addresses consist of a four octet network number and a six octet
   host number.  IPX uses the network number to route each packet
   through the IPX internet to the destination network.  Once the packet
   arrives at the destination network, IPX uses the six octet host
   number as the hardware address on that network.

   Host numbers are also exchanged in the IPX headers of packets of
   IPX's Routing Information Protocol (RIP).  This supplies end nodes
   and routers alike with the hardware address information required for
   forwarding packets across intermediate networks on the way towards
   the destination networks.

   For implementations of this memo, the first two octets of the host
   number will always be zero and the last four octets will be the
   node's four octet IP address.  This makes address mapping trivial for
   unicast transmissions: the first two octets of the host number are
   discarded, leaving the normal four octet IP address.  The
   encapsulation code should use this IP address as the destination
   address of the UDP/IP tunnel packet.

Broadcasts between Peer Servers

   IPX requires broadcast facilities so that NetWare servers and IPX
   routers sharing a network can find one another.  Since internet-wide
   IP broadcast is neither appropriate nor available, some other
   mechanism is required.  For this memo, each server and router should
   maintain a list of the IP addresses of the other IPX servers and



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