inet(7) inet(7)
NAME
inet - Internet protocol family
SYNOPSIS
#include <sys/types.h>
#include <netinet/in.h>
DESCRIPTION
The Internet protocol family implements a collection of
protocols which are centered around the Internet Protocol (IP)
and which share a common address format. The Internet family
protocols can be accessed via the socket interface, where they
support the SOCK_STREAM, SOCK_DGRAM, and SOCK_RAW socket
types, or the Transport Level Interface (TLI), where they
support the connectionless (T_CLTS) and connection oriented
(T_COTS_ORD) service types.
Protocols
The Internet protocol family comprises the Internet Protocol
(IP), the Address Resolution Protocol (ARP), the Internet
Control Message Protocol (ICMP), the Transmission Control
Protocol (TCP), and the User Datagram Protocol (UDP).
TCP supports the socket interface's SOCK_STREAM abstraction
and TLI's T_COTS_ORD service type. UDP supports the
SOCK_DGRAM socket abstraction and the TLI T_CLTS service type.
See TCP(7) and UDP(7). A direct interface to IP is available
via both TLI and the socket interface; See IP(7). ICMP is
used by the kernel to handle and report errors in protocol
processing. It is also accessible to user programs [see
ICMP(7)]. ARP is used to translate 32-bit IP addresses into
48-bit Ethernet addresses [see ARP(7)].
The 32-bit IP address is divided into network number and host
number parts. It is frequency-encoded; The most-significant
bit is zero in Class A addresses, in which the high-order 8
bits represent the network number. Class B addresses have
their high order two bits set to 10 and use the high-order 16
bits as the network number field. Class C addresses have a
24-bit network number part of which the high order three bits
are 110. Rather than using the default class A, B, or C
address, a subnet mask can be used for the network interface.
Subnet addressing is enabled and examined by the following
ioctl(2) commands; They have the same form as the SIOCSIFADDR
command [see if(7)].
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inet(7) inet(7)
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.
Addressing
IP addresses are four byte quantities, stored in network byte
order. IP addresses should be manipulated using the byte
order conversion routines [see byteorder(3N)].
Addresses in the Internet protocol family use the following
structure:
struct sockaddr_in {
short sin_family;
ushort_t sin_port;
struct in_addr sin_addr;
char sin_zero[8];
};
Library routines are provided to manipulate structures of this
form; See inet(3N).
The sin_addr field of the sockaddr_in structure specifies a
local or remote IP address. Each network interface has its
own unique IP address. The special value INADDR_ANY may be
used in this field to effect wildcard matching. Given in a
bind(3N) call, this value leaves the local IP address of the
socket unspecified, so that the socket will receive
connections or messages directed at any of the valid IP
addresses of the system. This can prove useful when a process
neither knows nor cares what the local IP address is or when a
process wishes to receive requests using all of its network
interfaces. The sockaddr_in structure given in the bind(3N)
call must specify an in_addr value of either IPADDR_ANY or one
of the system's valid IP addresses. Requests to bind any
other address will elicit the error EADDRNOTAVAI. When a
connect(3N) call is made for a socket that has a wildcard
local address, the system sets the sin_addr field of the
socket to the IP address of the network interface that the
packets for that connection are routed via.
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inet(7) inet(7)
The sin_port field of the sockaddr_in structure specifies a
port number used by TCP or UDP. The local port address
specified in a bind(3N) call is restricted to be greater than
IPPORT_RESERVED (defined in <netinet/in.h>) unless the
creating process is running as the super-user, providing a
space of protected port numbers. In addition, the local port
address must not be in use by any socket of same address
family and type. Requests to bind sockets to port numbers
being used by other sockets return the error EADDRINUSE. If
the local port address is specified as 0, then the system
picks a unique port address greater than IPPORT_RESERVED. A
unique local port address is also picked when a socket which
is not bound is used in a connect(3N) or sendto [see send(3N)]
call. This allows programs which do not care which local port
number is used to set up TCP connections by simply calling
socket(3N) and then connect(3N), and to send UDP datagrams
with a socket(3N) call followed by a sendto [see send(3N)]
call.
Although this implementation restricts sockets to unique local
port numbers, TCP allows multiple simultaneous connections
involving the same local port number so long as the remote IP
addresses or port numbers are different for each connection.
Programs may explicitly override the socket restriction by
setting the SO_REUSEADDR socket option with setsockopt [see
getsockopt(3N)].
TLI applies somewhat different semantics to the binding of
local port numbers. These semantics apply when Internet
family protocols are used via the TLI.
REFERENCES
ARP(7), bind(3N), byteorder(3N), connect(3N), ICMP(7), if(7),
ioctl(2), IP(7), gethostent(3N), getnetent(3N),
getprotoent(3N), getservent(3N), getsockopt(3N), send(3N),
socket(3N), TCP(7), UDP(7)
Network Information Center DDN Protocol Handbook (3 vols.)
NOTICES
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.
Copyright 1994 Novell, Inc. Page 3