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
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 <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 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 4.3BSD Interprocess Communication Tutorial" (see
MachTen Programmer’s Guide)

"An Advanced 4.3BSD Interprocess Communication Tutorial" (see
MachTen Programmer’s Guide)

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.