IPX packet structure

The structure of an IPX packet is identical to that of an XNS packet. The packet header consists of 30-bytes. The minimum packet size is 30 bytes (header only), while the maximum size is Maximum Transmission Unit minus the 30-byte header (MTU-30).

Some of the fields in the header are byte-order sensitive, and the data must be sent in hi-lo order (network), as illustrated in ``Byte order'' below.

Byte order

``IPX packet structure'' illustrates the IPX packet structure.

IPX packet structure

Although the IPX packet header has the format as shown in ``IPX packet structure'', there are frame-specific differences in the placement of the IPX header. The frame type is the format of the MAC (Media Access Control) header. The MAC header is specific to each transport and frame type. For example, IPX recognizes the following Ethernet frame types:

802.3 Raw

The IPX header follows immediately after the Length field in the MAC header.

IEEE 802.2

The IPX header follows immediately after the IEEE 802.2 header (DSAP, SSAP, and Control).

Ethernet II

The Type field in the MAC header has a value of 8137, and the IPX header follows immediately after the Type field.

Ethernet SNAP

The IPX header follows immediately after the 5-byte protocol identifier field.

• Token ring

• Token ring SNAP

For example, Ethernet supports 1500-byte packets, where 30 bytes is the IPX header and 1470 bytes is the actual data. In some cases, the maximum data size is limited by routers connecting LANs. Some older Ethernet routers limit the maximum IPX packet size to 576 bytes.

The content and structure of the data portion are entirely the responsibility of the application using IPX and can take any format.