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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 Inter-
     net 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 pack-
		     ets/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 pack-
		     ets.  Defaults to false.

     log_redirect    (boolean) Enable/disable logging of ICMP Redirect pack-
		     ets.  Defaults to false.

     bmcastecho      (boolean) Enable/disable ICMP replies received via broad-
		     cast 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.

     [ENOTCONN] 	when trying to send a datagram, but no destination
			address is specified, and the socket hasn't been con-
			nected;

     [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 net-
			work 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 5.4			March 21, 2003			   FreeBSD 5.4

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