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 using 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 use the following addressing
structure,
struct sockaddr_in {
uint8_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 comprises 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 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
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),
icmp(4),
intro(4),
ip(4),
netintro(4),
tcp(4),
udp(4)
Stuart Sechrest, An
Introductory 4.4BSD Interprocess Communication Tutorial. (see
/usr/share/doc/psd/20.ipctut)
Samuel J. Leffler,
Robert S. Fabry, William N.
Joy, Phil Lapsley, Steve
Miller, and Chris Torek,
Advanced 4.4BSD IPC Tutorial. (see
/usr/share/doc/psd/21.ipc)
HISTORY
The
inet protocol interface appeared in
4.2BSD.
BUGS
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.