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

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INET(4) 			   BSD Kernel Interfaces Manual 			  INET(4)

NAME
     inet -- Internet protocol family

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

DESCRIPTION
     The Internet protocol family is a collection of protocols layered atop the Internet Protocol
     (IP) transport layer, and utilizing the Internet address format.  The Internet family pro-
     vides protocol support for the SOCK_STREAM, SOCK_DGRAM, and SOCK_RAW socket types; the
     SOCK_RAW interface provides access to the IP protocol.

ADDRESSING
     Internet addresses are four byte quantities, stored in network standard format (on the VAX
     these are word and byte reversed).  The include file <netinet/in.h> defines this address as
     a discriminated union.

     Sockets bound to the Internet protocol family utilize the following addressing structure,

	   struct sockaddr_in {
		   short   sin_family;
		   u_short sin_port;
		   struct  in_addr sin_addr;
		   char    sin_zero[8];
	   };

     Sockets may be created with the local address INADDR_ANY to effect ``wildcard'' matching on
     incoming messages.  The address in a connect(2) or sendto(2) call may be given as INADDR_ANY
     to mean ``this host''.  The distinguished address INADDR_BROADCAST is allowed as a shorthand
     for the broadcast address on the primary network if the first network configured supports
     broadcast.

PROTOCOLS
     The Internet protocol family is comprised of the IP transport protocol, Internet Control
     Message Protocol (ICMP), Transmission Control Protocol (TCP), and User Datagram Protocol
     (UDP).  TCP is used to support the SOCK_STREAM abstraction while UDP is used to support the
     SOCK_DGRAM abstraction.  A raw interface to IP is available by creating an Internet socket
     of type SOCK_RAW.	The ICMP message protocol is accessible from a raw socket.

     The 32-bit Internet address contains both network and host parts.	It is frequency-encoded;
     the most-significant bit is clear in Class A addresses, in which the high-order 8 bits are
     the network number.  Class B addresses use the high-order 16 bits as the network field, and
     Class C addresses have a 24-bit network part.  Sites with a cluster of local networks and a
     connection to the Internet may chose to use a single network number for the cluster; this is
     done by using subnet addressing.  The local (host) portion of the address is further subdi-
     vided into subnet and host parts.	Within a subnet, each subnet appears to be an individual
     network; externally, the entire cluster appears to be a single, uniform network requiring
     only a single routing entry.  Subnet addressing is enabled and examined by the following
     ioctl(2) commands on a datagram socket in the Internet domain; they have the same form as
     the SIOCIFADDR command (see intro(4)).

     SIOCSIFNETMASK  Set interface network mask.  The network mask defines the network part of
		     the address; if it contains more of the address than the address type would
		     indicate, then subnets are in use.

     SIOCGIFNETMASK  Get interface network mask.

SEE ALSO
     ioctl(2), socket(2), intro(4), tcp(4), udp(4), ip(4), icmp(4)

     "An Introductory 4.3 BSD Interprocess Communication Tutorial", PS1, 7.

     "An Advanced 4.3 BSD Interprocess Communication Tutorial", PS1, 8.

CAVEAT
     The Internet protocol support is subject to change as the Internet protocols develop.  Users
     should not depend on details of the current implementation, but rather the services
     exported.

HISTORY
     The inet protocol interface appeared in 4.2BSD.

4.2 Berkeley Distribution		   June 5, 1993 		4.2 Berkeley Distribution
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