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 provides 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 Proto-
     col (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