TCP/IP Clients Can't Connect to SNA Server on Windows NT 4.0 (161778)

SYMPTOMS

SNA Server client users may be unable to connect over TCP/IP sockets to the SNA Server when running on a multi-homed computer running Windows NT Server 4.0. This problem may occur after initially installing SNA Server, or after upgrading a working SNA Server system from Windows NT Server 3.51 to Windows NT Server 4.0.

SNA Server client computers running either Windows 3.x or Windows 95 may receive 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 45 seconds or more before getting a session through the server. This is caused by a timeout when attempting to connect with TCP/IP sockets, followed by a successful attempt to connect over named pipes.

NOTE: A server that has the TCP/IP protocol bound to more than one network adapter is referred to as "multi-homed." Each TCP/IP adapter binding is configured with a unique IP address connected to different logical subnets.

CAUSE

When SNA Server initializes, the first TCP/IP address returned by Windows sockets is advertised to SNA Server TCP/IP client computers over their "sponsor" connection. This TCP/IP address may be for an address on a disparate network from the client computer, or have an address that the client computer's default gateway does not know how to route.

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

Under Windows NT Server 4.0, the internal order of TCP/IP networks is determined by the order that TCP/IP initialization occurs over the network adapters. Therefore, there is no way to directly control the order that the TCP/IP addresses are registered on the SNA Server.

RESOLUTION

To resolve this problem, obtain the hotfix mentioned below. This update allows the administrator to specify which IP address should be advertised to 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 addresses configured for this server, try setting the Network to "1."

Note that this registry entry is already supported by SNA Server 3.0.

STATUS

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):

S E R V P A C K