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inet(7P)			   Protocols			      inet(7P)

       inet - Internet protocol	family

       #include	<sys/types.h>

       #include	<netinet/in.h>

       The Internet protocol family implements a collection of protocols which
       are centered around the Internet	Protocol ("IP")	and which share	a com-
       mon address format. The Internet	family protocols can be	accessed using
       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.

       The  Internet  protocol	family	is  comprised of 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(7P) and	udp(7P). A direct  in-
       terface to IP is	available using	both TLI and the socket	interface (see
       ip(7P)).	ICMP is	used by	the kernel to handle and report	errors in pro-
       tocol   processing.  It	is  also  accessible  to  user	programs  (see
       icmp(7P)). ARP is used to translate 32-bit  IP  addresses  into	48-bit
       Ethernet	addresses. See arp(7P).

       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 ad-
       dresses have a 24-bit network number part of which the high order three
       bits  are  110.	Sites with a cluster of	IP networks may	chose to use a
       single network number for the cluster; this is done by using subnet ad-
       dressing.  The host number portion of the address is further subdivided
       into subnet number and host number parts. Within	a subnet, each	subnet
       appears to be an	individual network. Externally,	the entire cluster ap-
       pears to	be a single, uniform network requiring only a  single  routing
       entry.  Subnet  addressing  is  enabled	and  examined by the following
       ioctl(2)	commands. They have the	same form as the SIOCSIFADDR command.

		    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.

       IP addresses are	four byte quantities, stored in	network	byte order. IP
       addresses should	be manipulated using the byte  order  conversion  rou-
       tines. See  byteorder(3SOCKET).

       Addresses  in  the Internet protocol family use the  sockaddr_in	struc-
       ture, which has that following members:

       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(3SOCKET).

       The  sin_addr  field  of	the sockaddr_in	structure specifies a local or
       remote IP address.  Each	network	interface has its own  unique  IP  ad-
       dress.	The  special value INADDR_ANY may be used in this field	to ef-
       fect "wildcard" matching. Given in a  bind(3SOCKET)  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(3SOCKET)	call must  specify  an
       in_addr	value of either	INADDR_ANY or one of the system's valid	IP ad-
       dresses.	Requests to bind any other address will	elicit the error  EAD-
       DRNOTAVAIL.  When a connect(3SOCKET) 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 through.

       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(3SOCKET)
       call is restricted to  be  greater  than	 IPPORT_RESERVED  (defined  in
       <<netinet/in.h>>)  unless  the creating process is running as the supe-
       ruser, 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(3SOCKET) or sendto  (see
       send(3SOCKET)) call. This allows	programs which do not care which local
       port number is used  to	set  up	 TCP  connections  by  simply  calling
       socket(3SOCKET)	and  then  connect(3SOCKET), and to send UDP datagrams
       with a socket(3SOCKET) call followed by a sendto() 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  num-
       bers  are  different for	each connection. Programs may explicitly over-
       ride the	socket restriction by setting the SO_REUSEADDR	socket	option
       with setsockopt (see getsockopt(3SOCKET)).

       TLI  applies  somewhat different	semantics to the binding of local port
       numbers.	  These	semantics apply	when  Internet	family	protocols  are
       used using the TLI.

       ioctl(2), bind(3SOCKET),	byteorder(3SOCKET), connect(3SOCKET), gethost-
       byname(3NSL),  getnetbyname(3SOCKET),   getprotobyname(3SOCKET),	  get-
       servbyname(3SOCKET),	    getsockopt(3SOCKET),	send(3SOCKET),
       socket(3SOCKET),	arp(7P), icmp(7P), ip(7P), tcp(7P), udp(7P)

       Network Information Center, DDN Protocol	Handbook  (3  vols.),  Network
       Information Center, SRI International, Menlo Park, Calif., 1985.

       The Internet protocol support is	subject	to change as the Internet pro-
       tocols develop.	Users should not depend	on details of the current  im-
       plementation, but rather	the services exported.

SunOS 5.9			  3 Aug	2000			      inet(7P)


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