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inet(7)


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) Version 4 and Version 6 transport layers, 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.

  Internet addresses are 4-byte (AF_INET) or 16-byte (AF_INET6) quantities,
  stored in network standard format (on the Alpha, VAX and other machines,
  these are word and byte reversed).  The netinet/in.h include file defines
  the in_addr and in6_addr (AF_INET6) structures to hold these addresses.

  Sockets bound to the Internet protocol family utilize an addressing
  structure sockaddr_in (AF_INET) or sockaddr_in6 (AF_INET6), whose format is
  dependent on whether _SOCKADDR_LEN has been defined prior to including the
  netinet/in.h header file.  If _SOCKADDR_LEN is defined, the sockaddr_in
  (AF_INET) or sockaddr_in6 (AF_INET6) structure takes 4.4BSD behavior, with
  a separate field for specifying the length of the address; otherwise, the
  default 4.3BSD behavior is used.

  Sockets may be created with the local address INADDR_ANY (AF_INET) or
  in6addr_any (AF_INET6) to effect wildcard matching on incoming messages.
  The address in a connect() or sendto() call may be given as INADDR_ANY
  (AF_INET) or in6addr_any (AF_INET6) to mean ``this host.''  The
  distinguished address INADDR_BROADCAST (AF_INET) is allowed as a shorthand
  for the broadcast address on the primary network if the first network
  configured supports broadcast.  There is no broadcast in IPv6.

  The Internet protocol family comprises the IP transport protocol, Internet
  Control Message Protocol (ICMP) Version 4 and Version 6, 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 IP Version 4 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 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.

  IPv4 subnet addressing is enabled and examined by the following ioctl
  commands on a datagram socket in the Internet domain; they have the same
  form as the SIOCSIFADDR command (see the reference page for the netintro
  function).

  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.

  The 128-bit IP Version 6 address has several formats.	 One format is as
  follows:

       x:x:x:x:x:x:x:x

  In this format, x is the hexadecimal value of a 16-bit piece of the
  address.  See the Network Programmer's Guide for more information on IPv6
  addresses.


NOTES

  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.


SEE ALSO

  Functions: ioctl(2), socket(2).

  Network Information: netintro(7), tcp(7), udp(7), ip(7), icmp(7)

  Network Programmer's Guide

  Technical Overview

  RFC 2373, IP Version 6 Addressing Architecture, July 1998

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