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  Asked: May 6 2008   7:22 PM GMT
  Asked by: WinComputingATE

How can I setup a DNS server to respond with an IP address when an A record doesn't exist?


DNS, DNS management, IP addressing

How can I setup Microsoft’s DNS server to respond with an IP address when an ‘A’ record does not exist?

For example, let’s say someone goes to

something.mydomain.com

but there’s no ‘A’ record for the subdomain, something.mydomain.com. Is it possible to still have Microsoft’s DNS Server respond with a valid (default) IP for the domain? I know that other DNS providers do provide this feature but I haven’t figured it out yet with Microsoft.

Thanks in advance for your time and consideration.

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Last Answered: May 6 2008  7:38 PM GMT  by Labnuke99




There always has to be an A type record at some point along the path. There can be a CNAME record that may resolve to a particular name that then resolves to the IP address of interest. Somewhere there has to be an authoritative nameserver for the domain that holds these records. There could also be header records on the website that redirects a visitor to particular content. This is dependent on the webserver.
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CosmoC  |   May 7 2008  3:48PM GMT

I don’t believe Microsoft DNS allows an asterisk in a host record name through the MMC DNS console. To create a wildcard A record you must create a subdomain named with an asterisk then create a blank A record in that subdomain. You can use the dnscmd.exe tool (or call the API directly).

dnscmd.exe DNSServerName /RecordAdd mydomain.com * A x.x.x.x

[If your Server is a 2000 box, you will need to enable LooseWildcarding first].

Wildcard A records are possible but using CNAME wildcards are usually a better way to go. Create an A record for all something.mydomain.com requests, then create a CNAME *.mydomain.com which points to it.

Keep in mind the HTTP HOST header will not get updated once it’s resolved. If madeup.mydomain.com gets forwarded to defaultsite.mydomain.com the header will remain madeup.mydomain.com. You will probably want to create a virtual host which redirects all ‘unknown’ hostnames to defaultsite.mydomain.com.