Single Sign-On Fails if the Windows NT Primary Domain Controller is Unavailable (235929)

SYMPTOMS

An APPC application configured to use SNA Server's Single Sign-On (SSO) Privileged Proxy feature may fail to connect to the host if the primary domain controller (PDC) where the primary Host Account Cache (HAC) is running becomes unavailable. The APPC application will receive an error message indicating an invalid User ID or Password was used when the problem occurs. For example, an ALLOCATE issued by an APPC application may fail with an error code of 080F6051 (AP_SECURITY_NOT_VALID).

NOTE: Applications using the standard SSO (not Privileged Proxy) feature may experience a similar problem if the fix described in the following Microsoft Knowledge Base article is not applied:

235381 SNA Server Access Violation While Determining Proxy Privilege

CAUSE

The SNA Server Host Security DLL (Snasii.dll) was originally designed to issue a GetDCName() call to locate a Windows NT Domain Controller so that it can determine what Windows NT groups the User ID specified by the application belongs to so that it can verify if the application's user context is authorized to make the request. The GetDCName() call always returns the name of the Windows NT PDC. The update discussed in article Q235381 includes a change such that the host security DLL calls GetAnyDCName() to do this same function. The GetAnyDCname() call returns the names of backup domain controllers (BDCs) as well as the PDC. The problem is that this call fails if the PDC is not available.

If the PDC is not available, the GetAnyDCName() fails, so the host security DLL is not able to verify if the application's user context is authorized to make the request that was received. The result is the invalid User ID or Password error being returned to the application.

RESOLUTION

To resolve this problem, obtain the latest service pack for SNA Server version 4.0. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

215838 How to Obtain the Latest SNA Server Version 4.0 Service Pack

MORE INFORMATION

The Host Security DLL is updated to call NetServerEnum() if the GetAnyDCName() fails. The NetServerEnum () call does successfully return if the PDC is not available. The Host Security DLL is also updated to allow it to reconnect to a backup HAC if the primary HAC it is communicating with fails for some reason. With this update applied, the Host Security DLL can switch from the primary HAC to a backup HAC if the primary goes down. It can also locate a backup HAC at startup, even if the primary HAC is not running. This "hot backup" feature has the following requirements:

The backup HAC databases must be running on BDCs. The Host Security DLL only looks for DCs. It does not look for Windows NT member servers.
A backup HAC database is useful only if it has been able to contact the primary HAC database to read its initial copy of the account database. All backup HAC services delete their copy of the HAC database when they are stopped.

For additional information about SNA Server's Single Sign-On Privileged Proxy feature, please see the following article in the Microsoft Knowledge Base:

165385 Single Signon for APPC Applications Using Privileged Proxy