INET(4F)																  INET(4F)

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 Inter-
       net 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: layed out as highest to lowest order bytes in memory or
       ``Big Endian'' (the VAX is word and byte reversed, or ``Little Endian''; the  PDP-11  is  byte  reversed  within  each  word,  or  ``Middle
       Endian'').  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 Pro-
       tocol (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(4N)).

       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(4N), tcp(4P), udp(4P), ip(4P), icmp(4P)

       An Introductory 4.3BSD Interprocess Communication Tutorial (PS1:7).

       An Advanced 4.3BSD Interprocess Communication Tutorial (PS1:8).

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.

4.2 Berkeley Distribution					  August 1, 1987							  INET(4F)