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I googled and found out that ICMP does not belong to the application layer.

Does this mean that even no OS is installed, a network card still knows how to reply an ICMP request?

Another situation is, when the computer is soft-powered off, some power is still reserved for the network card (so that it can support Wake-On-LAN), can the network card respond to ICMP request in this state?

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up vote 6 down vote accepted

Sure you could send an ICMP request to a NIC by itself, but where are you going to send it? How can the NIC maintain an IP address without any software controlling it? I'm going to have to say no on this one.

As for true Wake-On-LAN, the card only watches for magic packets. In Windows however, if you set the adapter to Allow this device to bring the computer out of standby, which is not exactly the same as BIOS-enabled Wake-On-LAN, a ping will work when the PC is in standby. It seems to bring the computer to a slightly elevated power state to respond, then goes back into sleep mode. For true Wake-On-LAN when the computer is shut off, a ping does not seem to work.

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There exist smart NICs that can be configured to handle portions of the IP stack, so I'll assume that ICMP can be configured/contained on the board. But those cards are the exception. In general, this won't work.

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ICMP belongs to Layer 3 of the stack. This is typically a software layer. What this means is that you will need to have some sort of software running, although it need not be a full fledge OS. All you need is a basic TCP/IP stack running, which can be embedded on the NIC card itself as an alternative. However, you need to have some sort of software running. The hardware generally takes care of Layer 2 and Layer 1 of the stack.

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Remember that the layer doesn't have anything to do with how it's implemented in hardware/software/firmware. Typically, the application layer isn't the only software layer - the operating system handles layers below it too.

There's nothing to prevent the card from implementing its own complete stack (including the application layer) while the operating system isn't running, but you'd only see this on the likes of remote access cards for server.

As John T has said, wake-on-lan isn't a full implementation: I would guess it implements the data link layer and a very restricted "network layer" which just checks for the magic packets.

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