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. 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 {
u_int8_t sin_len;
sa_family_t sin_family;
in_port_t sin_port;
struct in_addr sin_addr;
int8_t 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 Internet may choose 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
netintro(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), inet_net_ntop(3), inet_ntop(3), icmp(4), ip(4), netintro(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.
HISTORY
The inet protocol interface appeared in
4.2BSD.
CAVEATS
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.