icmp man page on OpenDarwin

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ICMP(4)			 BSD Kernel Interfaces Manual		       ICMP(4)

NAME
     icmp — Internet Control Message Protocol

SYNOPSIS
     #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 net‐
     work 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
     and recvfrom 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.

   Non-privileged ICMP
     ICMP sockets can be opened with the SOCK_DGRAM socket type without
     requiring root privileges. The synopsis is the following:

     socket(AF_INET, SOCK_DGRAM, IPPROTO_ICMP)

     This can be used by non root privileged processes to send ICMP echo
     requests to gauge the quality of the connectivity to a host, to receive
     ICMP destination unreachable message for path MTU discovery, or to
     receveive time exceeded message for traceroute.

     Datagram oriented ICMP sockets offer a subset of the functionality avail‐
     able to raw ICMP sockets. Only IMCP request messages of the following
     types can be sent: ICMP_ECHO, ICMP_TSTAMP or ICMP_MASKREQ.	 The code
     field must be the value zero (0).	The minimal length of an ICMP message
     request is eight (8) octets.

     The following IP level option can be used with datagram oriented ICMP
     sockets:

	 IP_OPTIONS
	 IP_HDRINCL
	 IP_TOS
	 IP_TTL
	 IP_RECVOPTS
	 IP_RECVRETOPTS
	 IP_RECVDSTADDR
	 IP_RETOPTS
	 IP_MULTICAST_IF
	 IP_MULTICAST_TTL
	 IP_MULTICAST_LOOP
	 IP_ADD_MEMBERSHIP
	 IP_DROP_MEMBERSHIP
	 IP_MULTICAST_VIF
	 IP_PORTRANGE
	 IP_RECVIF
	 IP_IPSEC_POLICY
	 IP_STRIPHDR

     When the IP option IP_HDRINCL is used, the provided IP header must obey
     the following rules:

	 ip_v	    Must be IPVERSION (4);
	 ip_hl	    Between 5 and 10 (inclusive);
	 ip_tos	    Any value;
	 ip_len	    Must be the total length of IP datagram (IP header + ICMP
		    message);
	 ip_id	    Must be zero, will be automatically set;
	 ip_off	    Must be zero, will be automatically set;
	 ip_ttl	    Any value;
	 ip_p	    Must be IPPROTO_IP;
	 ip_sum	    Value ignored, will be automatically set;
	 ip_src	    Must be an IP address currently assigned to one of the
		    local interface or INADDR_ANY;
	 ip_dst	    Any address;
	 ip_opts    Any option.

     The maximum length of a IMCP message that can be sent is controlled by
     the sysctl variable net.inet.raw.maxdgram.

DIAGNOSTICS
     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 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;

     [EINVAL]	      when an invalid value is used with IMCP datagram socket
		      for a field of the IP or ICMP header.

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

HISTORY
     The icmp protocol appeared in 4.3BSD.

4.3 Berkeley Distribution	 June 19, 2002	     4.3 Berkeley Distribution
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