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ICMP
ICMP is the network protocol for control and diagnostic messages, most famously used by ping.
Alongside carrying data, IP networks need to report problems and probe reachability; ICMP (Internet Control Message Protocol) handles that with messages like 'destination unreachable' and the echo request/reply that ping uses. It is not for application data but for the network talking about itself. Implementing it lets a stack respond to and issue those diagnostic messages.
See also
- GICThe GIC is ARM's Generic Interrupt Controller, the hardware that routes device interrupts to CPU cores.
- file descriptorA file descriptor is a small integer the operating system hands you to refer to an open file, socket, or other I/O channel.