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ICMP(4)                FreeBSD Kernel Interfaces Manual                ICMP(4)

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.

FreeBSD 11.0-PRERELEASE         March 21, 2003         FreeBSD 11.0-PRERELEASE

NAME | SYNOPSIS | DESCRIPTION | ERRORS | SEE ALSO | HISTORY

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