A. Unicast is any network communication between a single sender and a single receiver. DHCP server responses typically use multicast communication to broadcast to all DHCP clients within a limited broadcast address (e.g., 255.255.255.255). However, you can configure the registry on Windows NT 4.0 or later DHCP servers to let clients request a unicast response, rather than a multicast response, from the DHCP server by performing the following steps:

  1. Start a registry editor (e.g., regedit.exe).
  2. Navigate to the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DHCPServer\Parameters registry subkey.
  3. Double-click IgnoreBroadcastFlag (or create this value of type DWORD if it doesn't already exist).
  4. Set IgnoreBroadcastFlag to 1 to ignore the DHCP client request flag and always multicast responses or 0 to let the client choose between unicast or multicast, then click OK.
  5. Close the registry editor.
  6. Reboot the server.

Pre-NT 4.0 DHCP versions will ignore this registry setting.