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NAME

     icmp - Internet Control Message Protocol

SYNOPSIS

     #include <sys/types.h>
     #include <sys/socket.h>
     #include <netinet/in.h>

     int
     socket(AF_INET, SOCK_RAW, proto);

DESCRIPTION

     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.

   MIB Variables
     The ICMP protocol implements a number of variables in the net.inet.icmp
     branch of the sysctl(3) MIB.

     maskrepl        (boolean) Enable/disable replies to ICMP Address Mask
                     Request packets.  Defaults to false.

     maskfake        (unsigned integer) When maskrepl is set and this value is
                     non-zero, it will be used instead of the real address
                     mask when the system replies to an ICMP Address Mask
                     Request packet.  Defaults to 0.

     icmplim         (integer) Bandwidth limit for ICMP replies in
                     packets/second.  Used when icmplim_output is non-zero.
                     Defaults to 200.

     icmplim_output  (boolean) Enable/disable bandwidth limiting of ICMP
                     replies.  Defaults to true.

     drop_redirect   (boolean) Enable/disable dropping of ICMP Redirect
                     packets.  Defaults to false.

     log_redirect    (boolean) Enable/disable logging of ICMP Redirect
                     packets.  Defaults to false.

     bmcastecho      (boolean) Enable/disable ICMP replies received via
                     broadcast or multicast.  Defaults to false.

     reply_src       (str) An interface name used for the ICMP reply source in
                     response to packets which are not directly addressed to
                     us.  By default continue with normal source selection.

ERRORS

     A socket operation may fail with one of the following errors returned:

     [EISCONN]          when trying to establish a connection on a socket
                        which already has one, or when trying to send a
                        datagram with the destination address specified and
                        the socket is already connected;

     [ENOTCONN]         when trying to send a datagram, but no destination
                        address is specified, and the socket has not been
                        connected;

     [ENOBUFS]          when the system runs out of memory for an internal
                        data structure;

     [EADDRNOTAVAIL]    when an attempt is made to create a socket with a
                        network address for which no network interface exists.

SEE ALSO

     recv(2), send(2), inet(4), intro(4), ip(4)

HISTORY

     The icmp protocol appeared in 4.3BSD.