inet - Internet Protocol family
#include <sys/types.h> #include <netinet/in.h>
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). 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.
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.
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)
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