User Guide

Understanding 15
Internetwork Packet Exchange
103-000176-001
August 29, 2001
Novell Confidential
Manual 99a38 July 17, 2001
Sending nodes always set the Transport Control field to zero when
building an IPX packet. When a router receives a packet that requires
further routing, it increments this field by one and forwards the packet.
Packet Type —Type of service offered or required by the packet.
Novell currently uses the packet types listed in Table 1.
Table 1 Packet Types
Destination Network —Number of the network to which the destination
node is attached.
When a sending node sets this field to 0x0 (that is, 0x00000000), the
destination node is assumed to be on the same network segment as the
sending (or source) node.
A special case exists when a workstation sends SAP Get Nearest Server
and RIP Get Local Target (or Route Request) broadcast requests at
initialization time. Because the workstation does not yet know which
network it belongs to, it sets both the Source Network and Destination
Network fields to 0 for these requests. When a router receives one of these
requests, it sends a reply directly to the sending workstation, filling in the
Source Network and Destination Network fields with the appropriate
network numbers.
NOTE: IPX does not have a broadcast network number (such as 0xFFFFFFFF).
In addition to network number 0, the numbers 0xFFFFFFFF and
0xFFFFFFFE are reserved for specific purposes. For this reason, they
should not be assigned to any IPX network. For more information about
Packet Type Field Value (Hex) Purpose
NLSP 0x00 NLSP packets
Routing information 0x01 RIP packets
Service advertising 0x04 SAP packets
Sequenced 0x05 SPX packets
NCP 0x11 NCP packets
Propagated 0x14 NetBIOS and other
propagated packets