What Are “Magic Packets” for Waking Computers?

When you are tweaking or adjusting various settings on your computer, sooner or later you will likely run across some options that leave you puzzled or confused. With that in mind, today’s SuperUser Q&A post has the answers to a confused reader’s questions.

Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites.

The Question

SuperUser reader AlainD wants to know what magic packets for waking computers are:

My wireless adapter (Intel Dual Band Wireless-N 7260) has two settings inDevice Manager that I do not understand.

Wake on Magic Packet

Wake on Pattern Match

After a bit of research, I found this Microsoft TechNet article which defines the feature as follows:
WakeOnMagicPacket – Defines if a network adapter is enabled to wake a computer on the magic packet.

This rather cryptic description is a bit low on details. Can anyone help?

I would prefer that my laptop not be woken up remotely under any circumstances. I have disabled Allow this device to wake the computer on the Power Management tab, but these settings appear to be separate. Can I disable these two settings without negative consequences?

What are magic packets for waking computers?

The Answer

SuperUser contributors Sam3000 and Ben N have the answer for us. First up, Sam3000:

These two settings form a feature of most modern computers known as Wake on LAN. In a nutshell, leaving this setting on allows the network card of your system to receive sufficient power to remain in standby mode while the rest of the system is powered off. While in standby mode, it may receive a magic packet, a small amount of data specific to the MAC address of the network card, and will respond to this by turning on the system.

It is very useful for remote control situations, however, you may disable these features without any negative consequences. Kudos to you for doing some prior research as well. For further information, you can read this How-To Geek article:

Followed by the answer from Ben N:

Sam3000’s answer is very nice. I will add some technical details.

Wake on Magic Packet causes the network card to awaken the computer when it receives a magic packet. A packet is considered “magic” when it contains FF FF FF FF FF FF (six instances of the largest possible byte value) followed by sixteen instances of the card’s six-byte MAC address. That sequence can appear anywhere within the frame, so the packet can be sent over any higher-level protocol. Usually, UDP is used, but sometimes raw frames with EtherType 0x0842 are used. (Source: Wikipedia)

Wake on Pattern Match is a superset of the previous one (Wake on Magic Packet). It will cause the card to wake the machine when various things come in, including a magic packet, a NetBIOS name query, a TCP SYN packet (either TCPv4 or TCPv6), etc. Those last ones may require ARP offload to be enabled. (Source: TechNet)

If you do not want or need your computer to be woken up from anywhere else, you can disable both options.

Have something to add to the explanation? Sound off in the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.
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