IPX/SPX Configuration and Management Manual

Protocol Interfaces and Services for NonStop™
IPX/SPX
IPX/SPX Configuration and Management Manual—425731-001
A-5
IPX Packet Header Format
The NonStop™ IPX/SPX subsystem uses RIP to broadcast the NonStop™ Himalaya S-
series server’s network address onto the NetWare LAN. RIP is also used to collect the
addresses of other devices on the LAN and place them into the SAP table that is
maintained by the IPXPROTO process. If the network address of a client workstation
differs from the network address of the NonStop™ Himalaya S-series server, NonStop™
IPX/SPX uses the routing table to determine the best route by which to send data to the
client.
IPX Packet Header Format
An IPX packet header is 30 bytes. Figure A-3 shows the format of an IPX packet header.
Checksum
is set to FFFF (-1) by IPX implementations. This field is neither computed for
sending data nor checked when receiving data.
Packet Length
is the total length of the IPX header plus data. The maximum packet length is set by
the higher-level protocol layer (such as SPX or NCP). NonStop™ IPX/SPX imposes
this limit on the IPX packet size.
Transport Control
is used by IPX routers and denotes the number of routers an IPX packet crossed
(hops used). The originating station sets this field to 0.
Packet Type
specifies the higher-level protocol associated with the packet. IPX uses this field and
the socket number in the destination address to identify the process for which an
incoming packet is intended (see IPX Addresses on page A-6).
Table A-2
shows the possible values of the IPX Packet Type field and the associated
higher-level protocols.
Figure A-3. IPX Packet Header Format
019CDT .CDD
Check-
sum
Destination
Address
Source
Address
Packet
Length
Transport
Control
Data
Header
2
Byte
s
2
Byte
s
1
Byte
12
Bytes
4
Bytes
12
Bytes
Packet
Type
1
Byte