A. Windows XP and later OSs include the following services to support Universal Plug and Play (UPnP) devices:

  • the SSDP discovery service, which discovers UPnP devices on your network
  • the UPnP device host service, which provides support to host UPnP devices

Disabling these services doesn't guarantee that SSDP discovery messages will stop, and you might still see traffic on UDP port 1900. This problem can occur if Windows Messenger uses SSDP to identify upstream Internet gateway devices because Windows Messenger formats and sends its own SSDP traffic instead of using the built-in UPnP services. To stop this SSDP discovery traffic, perform the following steps:

  1. Start a registry editor (e.g., regedit.exe).
  2. Navigate to the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\DirectPlayNATHelp\DPNHUPnP subkey.
  3. From the Edit menu, select New, DWORD Value.
  4. Enter a name of UPnPMode and press Enter.
  5. Double-click the new value, set it to 2, then click OK.
  6. Close the registry editor.