Change UDP message size

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

You can use the following procedure to modify User Datagram Protocol (UDP) message size.


When you configure the UDP packet size to be larger than 512 bytes, remember that 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 maximum transmission unit (MTU), if possible — and configure your UDP hosts according to this maximum.


It is recommended that you do not directly edit the registry unless there is no other alternative. Modifications to the registry are not validated by the registry editor or by Windows before they are applied, and as a result, incorrect values can be stored. This can result in unrecoverable errors in the system. When possible, use Group Policy or other Windows tools, such as Microsoft Management Console (MMC), to accomplish tasks rather than editing the registry directly. If you must edit the registry, use extreme caution.

Administrative credentials

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 the Run as command to perform this procedure.

To change UDP message size

  1. Open Registry Editor.

  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 the DNS server.


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