Q193844: Explanation of DNS Wildcards

Article: Q193844
Product(s): Microsoft Windows NT
Version(s): WinNT:4.0
Operating System(s): 
Keyword(s): kbnetwork
Last Modified: 10-AUG-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft BackOffice Server 4.0 
- Microsoft Windows NT Server version 4.0 
-------------------------------------------------------------------------------

SUMMARY
=======

The Domain Name Service (DNS) can use wildcards to associate multiple possible
destination names with a single relay point or host.

MORE INFORMATION
================

Wildcards in DNS records are often used to forward mail to intranets that are
connected to the Internet by a host that acts as a mail gateway. The Internet
needs an MX record that will point all mail destined from the Internet to the
host that is acting as the relay.

The contents of the wildcard resource records conform with normal formats and
rules for resource records. Importantly, the asterisk (*) label always matches
at least one whole label and often multiple labels.

Wildcards are not used when the query name is known to exist. The closest match
will be used.

For example, the record

  *.EXAMPLE.MICROSOFT.COM. IN MX 10 MAIL1.EXAMPLE.MICROSOFT.COM.

would allow mail destined for the domains NEWYORK.EXAMPLE.MICROSOFT.COM and
MIAMI.FLORIDA.EXAMPLE.MICROSOFT.COM to be able to reach its destination through
the mail server MAIL1.EXAMPLE.MICROSOFT.COM.

NOTE: The asterisk (*) wildcard symbol must match at least one whole label.
E-mail destined to johndoe@EXAMPLE.MICROSOFT.COM would not use the above record
to arrive at its destination. An additional record, such as the following, would
be necessary:

  EXAMPLE.MICROSOFT.COM. IN MX 10 MAIL1.EXAMPLE.MICROSOFT.COM.

Additional query words: wildcards MX

======================================================================
Keywords          : kbnetwork 
Technology        : kbWinNTsearch kbWinNT400search kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbAudDeveloper kbBackOfficeSearch kbBackOfficeServ400
Version           : WinNT:4.0
Issue type        : kbinfo

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.