Explanation of DNS Wildcards

ID: Q193844

The information in this article applies to:

Microsoft BackOffice Server version 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
Version : WinNT:4.0
Platform : winnt
Issue type : kbinfo