inet - Internet protocol family


     #include <sys/types.h>

     #include <netinet/in.h>


     The Internet protocol family implements a collection of pro-
     tocols  which  are  centered  around  the  Internet Protocol
     ("IP") and which share a common 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 interface 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 protocol 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
     addresses 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 addressing. 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  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.
     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 routines. See  byteorder(3SOCKET).

     Addresses  in  the  Internet   protocol   family   use   the
     sockaddr_in structure, 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 address.  The special value INADDR_ANY may  be
     used in this field to effect "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 pro-
     cess 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  addresses.
     Requests  to  bind  any  other address will elicit the error
     EADDRNOTAVAIL. 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  superuser,
     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()

     Although this implementation  restricts  sockets  to  unique
     local port numbers, TCP allows multiple simultaneous connec-
     tions 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 res-
     triction by setting the SO_REUSEADDR socket option with set-
     sockopt (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),                       gethostbyname(3NSL),
     getnetbyname(3SOCKET),              getprotobyname(3SOCKET),
     getservbyname(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  protocols  develop.   Users  should  not depend on
     details of the current implementation, but rather  the  ser-
     vices exported.

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