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INET(4)		       FreeBSD Kernel Interfaces Manual		       INET(4)

     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 inter-
     face provides access to the IP protocol.

     Internet addresses	are four byte quantities, stored in network standard
     format.  The include file <netinet/in.h> defines this address as a	dis-
     criminated	union.

     Sockets bound to the Internet protocol family utilize the following ad-
     dressing 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 dis-
     tinguished	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 ab-
     straction.	 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 ad-
     dresses, 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 net-
     works 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 lo-
     cal (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 en-
     abled 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	sub-
		     nets are in use.

     SIOCGIFNETMASK  Get interface network mask.

     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.

     The inet protocol interface appeared in 4.2BSD.

     The Internet protocol support is subject to change	as the Internet	proto-
     cols develop.  Users should not depend on details of the current imple-
     mentation,	but rather the services	exported.

FreeBSD	13.0		       October 30, 2019			  FreeBSD 13.0


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