Explanation of DNS Wildcards

This article was previously published under Q193844
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SUMMARY
The Domain Name Service (DNS) can use wildcards to associate multiplepossible destination names with a single relay point or host.
MORE INFORMATION
Wildcards in DNS records are often used to forward mail to intranets thatare connected to the Internet by a host that acts as a mail gateway. TheInternet needs an MX record that will point all mail destined from theInternet to the host that is acting as the relay.

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

Wildcards are not used when the query name is known to exist. The closestmatch 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 andMIAMI.FLORIDA.EXAMPLE.MICROSOFT.COM to be able to reach its destinationthrough 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 aboverecord to arrive at its destination. An additional record, such as thefollowing, would be necessary:
   EXAMPLE.MICROSOFT.COM. IN MX 10 MAIL1.EXAMPLE.MICROSOFT.COM.				
wildcards MX
Properties

Article ID: 193844 - Last Review: 12/05/2015 09:25:09 - Revision: 1.1

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