INET(ADMP)                                 UNIX System V



     Name
          inet - Internet protocol family


     Syntax
          #include <sys/types.h>
          #include <netinet/in.h>


     Description
          The Internet protocol family is a set of protocols using the
          Internet  Protocol  (IP)  network  layer  and  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.


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

          Sockets bound  to  the  Internet  protocol  family  use  the
          following addressing structure:

            struct sockaddr_in {
                 short     sin_family;
                 u_short   sin_port;
                 struct    in_addr sin_addr;
                 char sin_zero[8];
            };

          When using sockets, the  sin_family  is  specified  in  host
          order, and the sin_port and sin_addr fields are specified in
          network order.

          Sockets may be created with the local address INADDR_ANY  to
          affect  wildcard  matching on incoming messages. The address
          in a connect(SSC) or sendto  [see  send(SSC)]  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.

          When using the Transport Layer  Interface  (TLI),  transport
          providers  such as tcp(ADMP) support addresses whose lengths
          vary from eight to sixteen bytes. The eight byte form is the
          same  as  a  sockaddr_in  without  the  sin_zero  field. The
          sixteen byte form is identical to sockaddr_in. Additionally,
          when  using  TLI, the sin_family field is accepted in either
          host  or  network  order.  For  communicating   with   other
          implementations  via  RFS, the preferred form is eight bytes
          with sin_family in network order.


     Protocols
          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;  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  choose
          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(S) commands on  a  datagram  socket  in  the
          Internet "communications domain"; they have the same form as
          the SIOCIFADDR command. [See intro(ADMP).]

     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
          rfsaddr(ADMP),    ioctl(S),    socket(SSC),     intro(ADMP),
          intro(SFF), icmp(ADMP), ip(ADMP), tcp(ADMP), udp(ADMP).


     Note
          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.


     (printed 8/17/89)                                  INET(ADMP)