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) 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.
Internet addresses are 4-byte quantities, stored in network standard format (on the VAX and other machines, these are word and byte reversed). The netinet/in.h include file defines this address as a discriminated union.
Sockets bound to the Internet protocol family utilize an addressing structure sockaddr_in, 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 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 to effect wildcard matching on incoming messages. The address in a connect() or sendto() 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.
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() 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 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)
Technical Overview delim off