3Com CoreBuilder 2500 User Manual - page 75
How IPX Routing Works
6-5
The packet includes the following elements:
■
Checksum
— A 16-bit checksum that is set to
1
s.
■
Packet length
— A 16-bit field that indicates the packet’s length in
bytes. This length includes both header and data. The length must be
at least
30
bytes.
■
Transport control
— A 1-byte field that indicates how many routers
a packet has passed through on its way to its destination. Packets are
discarded when this value reaches
16
. A network node sets this field
to
0
before the node sends the IPX packet.
■
Packet type
— A 1-byte field that specifies the upper-layer protocol
that receives the packet.
■
Destination network
— A 4-byte field that contains the destination
node network number. When a sending node sets this field to
0
, the
system routes the packet as if the sending and destination nodes are
on the same local segment.
■
Destination node
— A 6-byte field that contains the destination
node physical address.
■
Destination socket
— A 2-byte field that contains the socket address
of the packet’s destination process.
■
Source network
— A 4-byte field that contains the source node
network number. If a sending node sets this field to
0
, the source’s
local network number is unknown.
■
Source node
— A 6-byte field that contains the source node physical
address. Broadcast addresses are not allowed.
■
Source socket
— A 2-byte field that contains the socket address of
the process that transmitted the packet.
■
Packet data
— A field that contains information for upper-layer
network processes.
IPX Packet Delivery
Successful packet delivery depends on proper addressing and the
network configuration. The packet’s Media Access Control (MAC)
protocol header and IPX header address handle packet addressing.
The sending node must have the destination’s complete network address,
including the destination network, node, and socket. After the sending
node has the destination address, it can address the packet.