3Com 2500 manual The packet format consists of the following elements

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How IPX Routing Works 6-5

The packet format consists of the following elements:

Checksum — The IPX packet begins with a 16-bit checksum field that is set to 1s.

Packet Length — This 16-bit field contains the length, in bytes, of the complete network packet. This field includes both the IPX header and the data. The IPX length must be at least 30 bytes.

■Transport Control — This 1-byte field indicates how many routers a packet has passed through on its way to its destination. Packets are discarded when this value reaches 16. A sending node always sets this field to 0 when building an IPX packet.

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Packet Type — This 1-byte field specifies the upper-layer protocol that will receive the packet’s information.

Destination Network — This 4-byte field provides the destination node’s network number. When a sending node sets this field to zero, the destination node is assumed to be on the same local segment as the sending node.

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Destination Node — This 6-byte field contains the physical address of the destination node.

Destination Socket — This 2-byte field contains the socket address of the packet’s destination process.

Source Network — This 4-byte field provides the source node’s network number. If a sending node sets this field to 0, it means the source’s local network is unknown.

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Source Node — This 6-byte field contains the physical address of the source node. Broadcast addresses are not allowed.

Source Socket — This 2-byte field contains the socket address of the process that transmitted the packet.

Upper-layer Data — The data field contains information for the upper-layer processes.