TCP/IP Clients Can't Connect to SNA Server on Windows NT 4.0

This article was previously published under Q161778
This article has been archived. It is offered "as is" and will no longer be updated.
SNA Server client users may be unable to connect over TCP/IP sockets to theSNA Server when running on a multi-homed computer running Windows NT Server4.0. This problem may occur after initially installing SNA Server, or afterupgrading a working SNA Server system from Windows NT Server 3.51 toWindows NT Server 4.0.

SNA Server client computers running either Windows 3.x or Windows 95 mayreceive the following errors when attempting to open a session:
  • Users of 3270 may observe "No SNA Servers found in configuration." In an SNA Server 3270 message trace, the Open(SSCP) request will fail with the following error codes: err1: 0 (no servers found), and err2: 0 (no servers found).
  • APPC users may observe the following ALLOCATE error:
    primary_rc = 0xF004 (AP_COMM_SUBSYSTEM_NOT_LOADED)
    secondary_rc = 0xF0000001 or 0xF0000002
A client computer running Windows NT Workstation may observe a delay of 45seconds or more before getting a session through the server. This is causedby a timeout when attempting to connect with TCP/IP sockets, followed by asuccessful attempt to connect over named pipes.

NOTE: A server that has the TCP/IP protocol bound to more than one networkadapter is referred to as "multi-homed." Each TCP/IP adapter binding isconfigured with a unique IP address connected to different logical subnets.
When SNA Server initializes, the first TCP/IP address returned by Windowssockets is advertised to SNA Server TCP/IP client computers over their"sponsor" connection. This TCP/IP address may be for an address on adisparate network from the client computer, or have an address that theclient computer's default gateway does not know how to route.

This was not a problem under Windows NT Server 3.51 because the order ofthe TCP/IP addresses could be controlled by the TCP/IP protocol bindingorder within the Bindings dialog box (accessed in Control Panel Network).

Under Windows NT Server 4.0, the internal order of TCP/IP networks isdetermined by the order that TCP/IP initialization occurs over the networkadapters. Therefore, there is no way to directly control the order that theTCP/IP addresses are registered on the SNA Server.
To resolve this problem, obtain the hotfix mentioned below. This updateallows the administrator to specify which IP address should be advertisedto the SNA client computers in the following registry entry:
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\SnaBase   \Parameters\SnaTcp\    Network:REG_DWORD:<network number>				
where the default is 0. If there are two different TCP/IP addressesconfigured for this server, try setting the Network to "1."

Note that this registry entry is already supported by SNA Server 3.0.
Microsoft has confirmed this to be a problem in SNA Server versions 2.0,2.1, 2.11, and 3.0. This problem was corrected in the latest SNA Server version 2.11 U.S. Service Pack. For information on obtaining this Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):
prodsna multihomed

Article ID: 161778 - Last Review: 01/16/2015 18:28:43 - Revision: 4.0

  • Microsoft SNA Server 2.0
  • Microsoft SNA Server 2.1
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