Novell NETWARE 6, Руководство пользователя

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Internetwork Packet Exchange
Internetwork Packet Exchange
103-000176-001
August 29, 2001
Novell Confidential
Manual 99a
38
July 17, 2001
Figure 2 IPX Packet Structure
The following describes the IPX packet fields:
Š Checksum —Packet integrity check.
The checksum is used by the NetWare SFT
TM
III
TM
software and NetWare
4 software. Older versions of NetWare did not use the IPX checksum and
required that this field be set to 0xFFFF.
Š Packet Length —Length, in bytes, of the complete packet, which is the
length of the IPX header plus the length of the data.
The packet length is at least 30 bytes (for the IPX header).
Š Transport Control —Number of routers a packet has traversed on the way
to its destination.
IMPORTANT:
On a traditional, RIP-based IPX router, IPX packets whose
Transport Control field reaches a value of 16 are discarded. With NLSP, an IPX
packet can travel up to 127 hops to reach its destination. You make this possible
by setting the Hop Count Limit parameter from the Novell Internet Access Server
Configuration utility (NIASCFG). This enables you to limit the number of routers
(hops) an IPX packet traverses before it is discarded.
Checksum (2 bytes)
Packet Length (2 bytes)
Transport Control (1 byte)
Packet Type (1 byte)
Destination Network (4 bytes)
Destination Node (6 bytes)
Destination Socket (2 bytes)
Source Network (4 bytes)
Source Node (6 bytes)
Source Socket (2 bytes)
Higher-Level Protocol Headers
Data
MAC Header
Data
MAC Trailer
MAC Protocol Envelope
IPX Packet