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

by Wayne Maples [Published on 20 April 2004 / Last Updated on 20 April 2004]

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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