wake-on-lan | WOL is a cross-platform project | Automation library

When sending a wakeonlan packet, you need to make sure the target device can receive the packet.

At the moment, you are sending the packet to the IPv4 address of the device.

When your computer has to send a packet to an IPv4 address, it needs to know its MAC address. So it asks the network "Who has IPv4 192.168.2.32? Tell me your mac address". Since you TV is shutdown, it does not respond.

The real wake on lan packet will never be send, as it des not know the destination mac address.

The real question then becomes, why does it work directly after shutting down, and the reason for this is that your OS keeps a list of IPv4+mac address table, so it can quickly send the packet out. You can view this list with the command arp -av on Windows

Note how it shows "dynamic" when your program successfully wakes the TV, but shows "invalid" when it fails to wake the TV up.

One solution for this, is sending the packet to the broadcast IPv4 address, which every devices receives. This IPv4 address typically ends with .255 with typical consumer IPv4 ranges.

Long story short, ethtool is a means to display and adjust generic NIC/driver parameters (identification, the number of receive and transmit queues, receive and transmit offloads, you name it) in a userspace application. On the one side, there's kernel API which a NIC driver is connected to (in particular, by means of struct ethtool_ops). On the other side, there's an ioctl command named SIOCETHTOOL which a userspace application can use to send requests to the kernel side and get responses.

Sub-identifiers enumerating specific commands for SIOCETHTOOL exist, and they correspond to the methods of struct ethtool_ops. From the question of yours it follows that it's struct ethtool_ops that should be explained.

I suggest that you take a look at include/linux/ethtool.h. There's a comment section right before the definition of struct ethtool_ops. In particular:

^{Note: this answer only considers Linux, but the same should hold for any other system that implements UDP according to the IETF RFCs.}

You have to QUdpSocket::connectToHost and then QIODevice::write, e.g.