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Modify UDP message size

Updated: January 21, 2005

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

To modify UDP message size

  1. Open Registry Editor.


    • Incorrectly editing the registry may severely damage your system. Before making changes to the registry, you should back up any valued data on the computer. You can also use the Last Known Good Configuration startup option if you encounter problems after manual changes have been applied.

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


  3. Add the following DWORD entry:


  4. Type a maximum UDP packet size value in bytes.

    The default value is 1280 bytes. The value must be between 512 and 16384 in decimal format (200 and 4000 in hexadecimal format).

  5. Restart DNS server.


  • When configuring the UDP packet size to be larger than 512 bytes, remember UDP packets must travel through devices other than UDP hosts, such as routers, and these devices may not support UDP packets larger than 512 bytes. It is recommended that you establish the maximum UDP packet length support for all devices, and the path's MTU, if possible, and configure your UDP hosts according to this maximum.


  • To perform this procedure, you must be a member of the Administrators group on the local computer, or you must have been delegated the appropriate authority. If the computer is joined to a domain, members of the Domain Admins group might be able to perform this procedure. As a security best practice, consider using Run as to perform this procedure.

  • To open Registry Editor, click Start, click Run, type regedit, and then click OK.

  • For information on discovering the maximum transmission unit (MTU) of an arbitrary Internet path, see Request for Comment (RFC) 1191, "Path MTU Discovery."

Information about functional differences

  • Your server might function differently based on the version and edition of the operating system that is installed, your account permissions, and your menu settings. For more information, see Viewing Help on the Web.

See Also

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