Windows NT NWLink IPX/SPX: Network Number vs. Internal Network Number


NWLink IPX/SPX-compatible transport in Windows NT uses two different types of
network numbers. NT uses an IPX network number for routing purposes which is
assigned to each configured frame type and adapter combination on your computer.
This number is sometimes referred to as the “external network number,” and it
must be unique for each network segment. NT also uses an internal network number
for internal routing purposes which is also known as a “virtual network number.”
The internal network number uniquely identifies the computer on the
inter-network. These two network numbers serve two distinctly different
functions. : For more details, see Q150546

IPX/SPX stands for Internetwork Packet Exchange / Sequenced Packet Exchange.
NT’s implementation adds support for NetBIOS over IPX which is used for NT
browsing services. The internal network number is left at the default of
00000000 unless you are using File and Print Services for Netware or you have
enabled IPX routing.

The frame types are:


  • 802.2 format
    industry standard – default for Netware 3.12 and greater
  • 802.3 format
    Developed by Novell. Default for pre-3.12 Netware versions.

  • Ethernet_SNAP format
    802.3 with SNAP header
  • 802.5
    Token Ring
  • TokenRing_SNAP
    802.5 with SNAP header

When you configure the NWLink transport, you can chose auto-detect which
means NT will use the first frame type seen during its inpection period.
Auto-detect only works well in a homogenous, single frame environment. If no IPX
traffic is detected, 802.2 will be used. You should manually select the frame
type which is useful if there are multiple frame types being used and you need
to configure for multiple types.

SubNetwork Access Protocol (SNAP) used to transport Appletalk or SNA in IP or
IPX environments.

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