1INET(4F)                                                              INET(4F)
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NAME

6       inet - Internet protocol family
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SYNOPSIS

9       #include <sys/types.h>
10       #include <netinet/in.h>
11

DESCRIPTION

13       The  Internet protocol family is a collection of protocols layered atop
14       the Internet Protocol (IP) transport layer, and utilizing the  Internet
15       address  format.  The Internet family provides protocol support for the
16       SOCK_STREAM, SOCK_DGRAM, and SOCK_RAW socket types; the SOCK_RAW inter‐
17       face provides access to the IP protocol.
18

ADDRESSING

20       Internet addresses are four byte quantities, stored in network standard
21       format: layed out as highest to lowest order bytes in memory  or  ``Big
22       Endian''  (the VAX is word and byte reversed, or ``Little Endian''; the
23       PDP-11 is byte reversed within each word, or ``Middle  Endian'').   The
24       include  file  <netinet/in.h>  defines  this address as a discriminated
25       union.
26
27       Sockets bound to the Internet protocol  family  utilize  the  following
28       addressing structure,
29
30       struct sockaddr_in {
31              short     sin_family;
32              u_short   sin_port;
33              struct    in_addr sin_addr;
34              char      sin_zero[8];
35       };
36
37       Sockets  may  be  created  with  the local address INADDR_ANY to effect
38       “wildcard” matching on incoming messages.  The address in a  connect(2)
39       or  sendto(2)  call  may  be given as INADDR_ANY to mean ``this host.''
40       The distinguished address INADDR_BROADCAST is allowed  as  a  shorthand
41       for  the  broadcast address on the primary network if the first network
42       configured supports broadcast.
43

PROTOCOLS

45       The Internet protocol family is comprised of the IP transport protocol,
46       Internet Control Message Protocol (ICMP), Transmission Control Protocol
47       (TCP), and User Datagram Protocol (UDP).  TCP is used  to  support  the
48       SOCK_STREAM  abstraction  while  UDP  is used to support the SOCK_DGRAM
49       abstraction.  A raw interface to IP is available by creating an  Inter‐
50       net  socket  of type SOCK_RAW.  The ICMP message protocol is accessible
51       from a raw socket.
52
53       The 32-bit Internet address contains both network and host  parts.   It
54       is  frequency-encoded;  the  most-significant  bit  is clear in Class A
55       addresses, in which the high-order  8  bits  are  the  network  number.
56       Class  B addresses use the high-order 16 bits as the network field, and
57       Class C addresses have a 24-bit network part.  Sites with a cluster  of
58       local  networks and a connection to the DARPA Internet may chose to use
59       a single network number for the cluster; this is done by  using  subnet
60       addressing.   The local (host) portion of the address is further subdi‐
61       vided into subnet and host parts.  Within a subnet, each subnet appears
62       to  be an individual network; externally, the entire cluster appears to
63       be a single, uniform network requiring only  a  single  routing  entry.
64       Subnet  addressing  is  enabled  and examined by the following ioctl(2)
65       commands on a datagram socket in the Internet  domain;  they  have  the
66       same form as the SIOCIFADDR command (see intro(4N)).
67
68       SIOCSIFNETMASK      Set  interface  network  mask.   The  network  mask
69                           defines the network part of the address; if it con‐
70                           tains  more  of  the  address than the address type
71                           would indicate, then subnets are in use.
72
73       SIOCGIFNETMASK      Get interface network mask.
74

SEE ALSO

76       ioctl(2), socket(2), intro(4N), tcp(4P), udp(4P), ip(4P), icmp(4P)
77
78       An Introductory 4.3BSD Interprocess Communication Tutorial (PS1:7).
79
80       An Advanced 4.3BSD Interprocess Communication Tutorial (PS1:8).
81

CAVEAT

83       The Internet protocol support is subject to change as the Internet pro‐
84       tocols  develop.   Users  should  not  depend on details of the current
85       implementation, but rather the services exported.
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894.2 Berkeley Distribution       August 1, 1987                        INET(4F)
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