Gethostbyaddr() Call with Winsock2 Returns Address Pool Alias (192425)

SYMPTOMS

With Winsock2 installed, a user logging on to a Windows 95-based or Windows 98-based computer may not be authenticated by the Kerberos Network Authentication Service (typically implemented in UNIX-based or LINUX-based networks).

Additionally, clients in general may not be authenticated if the authentication is attempted using Microsoft Proxy Server.

This behavior is known to impact the use of Columbia University's Kermit- 95 communications software.

CAUSE

The Microsoft products to which this article applies cache Domain Name Service (DNS) name lookups. If an address pool alias is resolved using the Gethostbyname() call, the alias is cached for all returned addresses. Subsequent Gethostbyaddress() calls against any of the returned addresses are resolved to the alias, instead of to the actual computer name, until such time as the entry is removed from the cache (after 600 seconds, or being flushed to accommodate a new cache entry, if the cache is full).

The Kerberos client must request a service ticket using the actual name of the host to which it is connecting. A service ticket consists of binary data used to identify a user or service (similar in concept to Microsoft Windows NT access tokens). Use of the alias in place of the actual host name results in a service ticket being encoded with the wrong key. Retrieval of the actual host name is not possible under the above conditions when the initial name lookup for the server was performed against an address pool alias.

RESOLUTION

A supported fix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Apply it only to computers that are experiencing this specific problem. This fix may receive additional testing. Therefore, if you are not severely affected by this problem, Microsoft recommends that you wait for the next service pack that contains this hotfix.

To resolve this problem immediately, contact Microsoft Product Support Services to obtain the fix. For a complete list of Microsoft Product Support Services phone numbers and information about support costs, visit the following Microsoft Web site:

http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS

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 typical support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

This fix should have the following file attributes for Windows 95 and Windows 98 (note that the Windows 98 update is a single package that installs the correct component version for the indicated platforms):

File Name  Version    Date     Time     Size   Platform
-----------------------------------------------------------------------
Rnr20.dll  4.10.1658  09/08/98 04:58pm  43,008 Windows 95 (all versions)
Rnr20.dll  4.10.2003  06/26/99 07:11pm  43,520 Windows 98 
Rnr20.dll  4.10.2223  07/22/99 05:35pm  43,520 Windows 98 Second Edition

Note that on Windows 95, this updated component must be installed after the Winsock2 update is applied. There is currently no fix available for Microsoft Proxy server.

MORE INFORMATION

The third-party products discussed in this article are manufactured by vendors independent of Microsoft; we make no warranty, implied or otherwise, regarding these products' performance or reliability.

For more information about the Kerberos Network Authentication Service as discussed in RFC 1510, you can obtain a copy of RFC 1510 on the Internet from the following source:

ftp://ds.internic.net/rfc/rfc1510.txt

Additional information about the Kermit-95 product mentioned in this article is available on the Internet from the following sources:

http://www.columbia.edu/kermit
http://www.kermit-project.org/

The third-party contact information included in this article is provided to help you find the technical support you need. This contact information is subject to change without notice. Microsoft in no way guarantees the accuracy of this third-party contact information.

For additional information about Windows 98 and Windows 98 Second Edition hotfixes, click the article number below to view the article in the Microsoft Knowledge Base:

206071 General Information About Windows 98 and Windows 98 Second Edition Hotfixes

For additional information about Windows 95 hotfixes, click the article number below to view the article in the Microsoft Knowledge Base: