WOL (Wake on LAN) technology enables one to remotely switch On or switch Off a computer or a server using just the network port/network adapter. WOL could be useful for certain applications like,
- An administrator performing remote maintenance activities over LAN need not switch On or switch Off individual machines physically. They can just remotely switch it On, complete the maintenance activities and switch it Off, without leaving their desk.
- Some servers need not be always On. They can normally be kept in the switched Off state and switched On from anywhere, when required. This saves a lot of power, reduces the heat & wear and tear due to continuous operation.
- Sometimes, we leave a computer On just to access files from them over the Internet (from somewhere else), after a few hours. WOL enables us to shut-down the computer or keep it in hibernation until it is switched On from a remote location (only when required). This saves power, cooling and it is better for computers because they are generally not optimized for 24×7 operation.
A system being switched Off refers to the computer/server being shut-down, but the main AC power cord should still be connected to an electrical source and it should be switched On. This is required because, though the computer itself doesn’t draw any power when it is shut-down/in hibernation, the NIC (Network Interface Card) needs power to be able to continuously receive all the packets coming its way and recognize the special ‘magic packet’ that instructs it to start a system.
For WOL to work, it should be integrated into Network Interface Cards(NIC)/On-board NIC in the motherboard. Further, WOL needs to be enabled in the BIOS. Once the ‘magic packet’ containing the MAC address of the system to be switched On is received by the NIC (either from the LAN or from the WAN/Internet), it starts the procedure to switch On the system. Switching On refers to loading the BIOS, operating system and applications.
To use WOL, one might require administrative access to the system. WOL does not replace any user-names/passwords required to access the system and once switched On, it is similar to remote desktop that allows remote access to a system. A tutorial on how to enable Wake On LAN can be found here. Another tutorial for enabling WOL over the Internet (WAN) can be found here. It is even possible to Wake On Wireless LAN (WoWLAN) that uses the 802.11 Wi-Fi network to switch On or switch Off a system remotely.
There are a few limitations to the WOL protocol. For example, since WOL is a receive only protocol, there is no mechanism to send a confirmation packet, back to the initiator. Also, WOL is a broadcast protocol. So, routers should be configured to forward broadcasts.
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