3Com LANPLEX 2500, User Manual

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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 1 s.
■
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.
■
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.
■
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.
■
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.