Microsoft KB Archive/227943

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How Internet Information Services (IIS) Handles Reverse Lookup Failures

Article ID: 227943

Article Last Modified on 12/3/2007


  • Microsoft Internet Information Services 6.0
  • Microsoft Internet Information Server 4.0
  • Microsoft Internet Information Services 5.0

This article was previously published under Q227943

We strongly recommend that all users upgrade to Microsoft Internet Information Services (IIS) version 6.0 running on Microsoft Windows Server 2003. IIS 6.0 significantly increases Web infrastructure security. For more information about IIS security-related topics, visit the following Microsoft Web site:


IIS can perform access restrictions based on IP address, IP range, and DNS name. If you are performing IP restrictions based on the DNS name, it requires that IIS perform a reverse DNS lookup. If reverse DNS lookup fails (for example failure to access the DNS server) then the request is refused.


Note: You may need to restart IIS in some instances if the reason for the lookup failure is corrupted DNS entries.

Keywords: kbprb kbpending KB227943