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Configure EDNS0


You can use the following procedure to modify EDNS0 configuration. The value of the registry key EDNSCacheTimeout determines how long the Domain Name System (DNS) server keeps information about the extension mechanisms for DNS (EDNS) versions that are supported by other DNS servers that have responded to a query with an OPT resource record.

You can perform this procedure by using Registry Editor or by using the Dnscmd command-line tool.


Administrative credentials


Configuring EDNS0

To configure EDNS0 using the Windows interface
  1. Open Registry Editor.

  2. In Registry Editor, navigate to the following registry subkey:


  3. Add the following DWORD entry:


  4. To change the cache timeout, type a value in seconds between 3600 (1 hour) and 15724800 (182 days).

  5. In the same registry subkey (Parameters), add the following DWORD entry:


  6. To configure the DNS server to include an OPT resource record only in response to EDNS0 requests containing OPT resource records, type 0x1 (DWORD).

  7. Restart the DNS server.


To modify EDNS0 configuration using the command line
  • At a command prompt, type one of the following commands, and then press ENTER:

    • dnscmd ServerName /Config /EDNSCacheTimeout Value

    • dnscmd ServerName /Config /EnableEDNSProbes Value


    Value Description




    Required. Specifies the command to configure the DNS server.


    Required. Specifies the length of time that the DNS server remembers the EDNS parameters remote servers report.


    Required. Specifies whether or not the DNS server probes other DNS servers to determine if they support EDNS.


    Required. For /EDNSCacheTimeout, type a value in seconds between 3600 (1 hour) and 15724800 (182 days). For /EnableEDNSProbes, type 1 to configure the DNS server to probe other DNS servers and determine if they support EDNS. Type 0 to configure the DNS server to not probe remote servers for EDNS support. If you type 0, the DNS server will continue to use EDNS if other servers request it.

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