RFC 1234 (rfc1234) - Page 2 of 6
Tunneling IPX traffic through IP networks
Alternative Format: Original Text Document
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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