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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 provides protocol sup-port support
     port 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 Proto-col Protocol
     col (ICMP), Transmission Control Protocol (TCP), and User Datagram Protocol (UDP).  TCP is used to sup-port support
     port the SOCK_STREAM abstraction while UDP is used to support the SOCK_DGRAM abstraction.  A raw inter-face interface
     face 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 mostsignificant
     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 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 fol-lowing following
     lowing 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), icmp(4), intro(4), ip(4), tcp(4), udp(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