inet(7)inet(7)NAMEinet - 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) quanti‐
ties, 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 for‐
mat 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 mes‐
sages. 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 pro‐
tocol 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 address‐
ing. 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 sin‐
gle, 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). 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.
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 pro‐
tocols 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
inet(7)