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OpenDarwin 7.2.1 - man page for icmp (opendarwin section 4)

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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 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
     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 privi-
     leges. 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 available 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 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;

     [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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