Understanding the network.pdf - Back to Home

Figure 3.13. IPX datagram format.
• Checksum is a 16-bit field. Checksumming is not enabled by default in IPX,
so the field is often unused and set to a default (FFFF). IPX relies on Layer 2
for error checking.
• Packet length is a 16-bit descriptor expressing the size of the entire IPX
packet.
• Transport control is an 8-bit value that describes the number of hopsan IP
packet has traversed. It is decremented by 1 each time it passes through a
router. When 16 is reached, this is the maximum hop count for an IPX
network, and the packet is dropped.
• Packet type is used to indicate the kind of data contained in the datagram. 0
= Unknown, 1 = RIP, 4 = SAP, 5 = SPX, 17 = NCP, 20 = NetBIOS.
• Destination network is a 32-bit field. If the sender is local, this value is 0.
• Destination node is a 48-bit field. Unicast messages use the MAC/IPX
address of the destination end-node. Broadcast messages use all zeros.
• Destination port is a 16-bit field that indicates the ULP service port
destination address.
• Source network is a 32-bit field. A 0 here indicates that the datagram is
either unknown or a network broadcast.
• Source node is a 48-bit field, indicating the sender's address.