INET(4)                   386BSD Programmer's Manual                   INET(4)

NAME
     inet - Internet protocol family

MODULE
     inet <afidx>.

SYNOPSIS
     Makefile:
     $(NONSTDINC) += $(INCNET)

     C:
     #include <sys/types.h>
     #include "in.h"

DESCRIPTION
     The inet(4) module implements the core protocols of the Internet protocol
     family.  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
     <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 DARPA 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 subdivided 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       March 28, 1991                               2