Caching-Only DNS Server Incorrectly Reports "Name Error" on Wildcard MX Lookups

ID: Q192407

The information in this article applies to:

SYMPTOMS

A caching-only DNS server incorrectly returns a "Name Error" message when looking up a wildcard MX record. This occurs when another computer has recently looked up an "A" record with the same node name, and the "A" record is nonexistent. The record is held in cache on the caching-only server, and marked as Name Error. Future wildcard "MX" record lookups for the node name return Name Error until the cache is flushed on the caching- only DNS server.

Some UNIX mail servers query for a type "A" host name before querying for an "MX" record and, therefore, may not be able to properly deliver mail when Name Error is returned.


CAUSE

When the initial type "A" lookup is performed, the authoritative server replies with a "Name Error" message. The caching-only name server responds correctly by keeping this Name Error information in cache so that additional lookups do not require additional referrals from the authoritative DNS Server. When the wildcard "MX" request is received following the type "A" lookup, the caching server reads from cache and returns "Name Error" for the node.

Only in the wildcard MX record case, where the "A" record would be nonexistent while the MX record would be resolvable, would an incorrect error be generated.


RESOLUTION

A supported fix that corrects this problem is now available from Microsoft, but has not been fully regression tested and should be applied only to systems experiencing this specific problem. If you are not severely affected by this specific problem, Microsoft recommends that you wait for the next Windows NT service pack that contains this fix.

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 on support costs, please go to the following address on the World Wide Web:

http://support.microsoft.com/support/supportnet/default.asp
The English version of this fix should have the following file attributes or later: 


   Date      Time                 Size    File Name     Platform
   -------------------------------------------------------------
   08/22/98  12:48p               176,912 Dns.exe       (x86)
   08/22/98  01:04p                65,808 Nslookup.exe  (x86)

   08/22/98  12:47p               297,744 Dns.exe       (Alpha)
   08/22/98  01:02p                93,456 Nslookup.exe  (Alpha)

NOTE: If you contact Microsoft to obtain this fix, a fee may be charged. This fee is refundable if it is determined that you only require the fix you requested. However, this fee is non-refundable if you request additional technical support.

For more information about eligibility for no-charge technical support, see the following article in the Microsoft Knowledge Base:

Q154871 Determining If Your Product Is Eligible for No-Charge Technical Support
With the above fix, the authoritative name server responds to a query for a nonexistent hostname with error code 0. The caching-only server does not cache the name with error code 0, "No Error."

Please note that Dns.exe must be replaced on the authoritative server.


STATUS

Microsoft has confirmed this to be a problem in Windows NT version 4.0. 


Keywords          : kbbug4.00 kbfix4.00 
Version           : WinNT:4.0
Platform          : winnt 
Issue type        : kbbug

Last Reviewed: February 18, 1999