Proxy Client Does Not Correctly Handle a Second Call to WSALookupServiceBegin() After a Call Generates WSAEFAULT


Programs that use Winsock functions (such as Gethostbyname) may have unexpected problems or behaviors when they run on computers with the Winsock Proxy 2.0 client. The problems occur when a Winsock function that would otherwise succeed does not work because of a problem in the Winsock Proxy 2.0 client.

For example, Microsoft Exchange 2000 Server services may not start, or the Internet Mail service in Exchange Server may not send mail because LDAP DNS queries for the local domain controllers do not succeed. The query does not succeed because the call to Gethostbyname returns a "host not found" error even if the host is really available.


Winsock calls may not work because the Proxy client does not correctly handle a second call to WSALookupServiceBegin after a call does not work and generates WSAEFAULT.


To work around this issue, use any of the following methods:

  • Uninstall the Winsock Proxy 2.0 client.
  • Upgrade to Microsoft Internet Security and Acceleration (ISA) Server 2000.
  • Edit the Mspclnt.ini file in the Mspclnt share on the Proxy server and add the local namespaces that need to be resolved by using a LocalDomains=namespace entry under the [common] section. To do this:
    1. Open the Mspclnt.ini file in the Mspclnt share on the Proxy server. Under the [common] section, add a line with this text:
      Separate multiple namespaces by using a comma. For example:

    2. Restart the Winsock Proxy service on the Proxy server.
    3. On the Proxy client computer, update the proxy client settings in Control Panel by clicking Update in the WSP tool.
    4. Reboot the client computer that is running the Proxy client.
    NOTE: This workaround assumes that the client software is attempting to resolve local namespaces only. Any program on the client computer that needs to resolve external addresses may still encounter the symptoms that are described earlier in this article. For additional information, click the article number below
    to view the article in the Microsoft Knowledge Base:

    280833 Failure to Specify All DNS Zones in Proxy Client Leads to DNS Failures That Are Difficult to Track


A supported hotfix is now available from Microsoft, but it is only intended to correct the problem that this article describes. Apply it only to systems that are experiencing this specific problem.

To resolve this problem, contact Microsoft Product Support Services to obtain the hotfix. For a complete list of Microsoft Product Support Services telephone numbers and information about support costs, visit the following Microsoft Web site:Note In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

The English version of this fix should have the following file
attributes or later:

Date Time Version Size File name Platform
31-May-2001 17:39 2.0.390.16 141,584 Wspwsp.dll Intel

NOTE: This is a Winsock Proxy client fix; install it on computers that have the Winsock Proxy 2.0 client installed. You should also extract the files from the hotfix package and use them to update the files in the Mspclnt share on the Proxy 2.0 server. (Typically, this share is located in the Msp\Clients\I386 folder.) This allows new clients, and existing clients that run the reinstallation process, to receive the updated files.

To extract files from the Microsoft Windows NT 4.0 hotfix package, run the package and extract to a temporary folder. To extract files from the Microsoft Windows 2000 hotfix package, run the hotfix installer with the /c /t:path /x switches. For example, use this command:
q278337_w2k_sp3_x86_en.exe /c /t:c:\temp /x


Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.

Artikelnummer: 278337 – Letzte Überarbeitung: 14.02.2017 – Revision: 1

Microsoft Proxy Server 2.0 Standard Edition