ICMP is the error and control message protocol used by IP and the Internet protocol family. It may be accessed through a “raw socket” for network monitoring and diagnostic functions. The
proto parameter to the socket call to create an ICMP socket is obtained from
getprotobyname(3). ICMP sockets are connectionless, and are normally used with the
sendto(2) and
recvfrom(2) calls, though the
connect(2) call may also be used to fix the destination for future packets (in which case the
read(2) or
recv(2) and
write(2) or
send(2) system calls may be used).
Outgoing packets automatically have an IP header prepended to them (based on the destination address). Incoming packets are received with the IP header and options intact.