bsd/man/man4/udp.4

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  34 .\"     @(#)udp.4       8.1 (Berkeley) 6/5/93
  35 .\"
  36 .Dd June 5, 1993
  37 .Dt UDP 4
  38 .Os BSD 4.2
  39 .Sh NAME
  40 .Nm udp
  41 .Nd Internet User Datagram Protocol
  42 .Sh SYNOPSIS
  43 .Fd #include <sys/socket.h>
  44 .Fd #include <netinet/in.h>
  45 .Ft int
  46 .Fn socket AF_INET SOCK_DGRAM 0
  47 .Sh DESCRIPTION
  48 .Tn UDP
  49 is a simple, unreliable datagram protocol which is used
  50 to support the
  51 .Dv SOCK_DGRAM
  52 abstraction for the Internet
  53 protocol family.
  54 .Tn UDP
  55 sockets are connectionless, and are
  56 normally used with the
  57 .Xr sendto
  58 and
  59 .Xr recvfrom
  60 calls, though the
  61 .Xr connect 2
  62 call may also be used to fix the destination for future
  63 packets (in which case the
  64 .Xr recv 2
  65 or
  66 .Xr read 2
  67 and
  68 .Xr send 2
  69 or
  70 .Xr write 2
  71 system calls may be used).
  72 .Pp
  73 .Tn UDP
  74 address formats are identical to those used by
  75 .Tn TCP .
  76 In particular
  77 .Tn UDP
  78 provides a port identifier in addition
  79 to the normal Internet address format.  Note that the
  80 .Tn UDP
  81 port
  82 space is separate from the
  83 .Tn TCP
  84 port space (i.e. a
  85 .Tn UDP
  86 port
  87 may not be
  88 .Dq connected
  89 to a
  90 .Tn TCP
  91 port).  In addition broadcast
  92 packets may be sent (assuming the underlying network supports
  93 this) by using a reserved
  94 .Dq broadcast address ;
  95 this address
  96 is network interface dependent.
  97 .Pp
  98 Options at the
  99 .Tn IP
 100 transport level may be used with
 101 .Tn UDP ;
 102 see
 103 .Xr ip 4 .
 104 .Sh DIAGNOSTICS
 105 A socket operation may fail with one of the following errors returned:
 106 .Bl -tag -width [EADDRNOTAVAIL]
 107 .It Bq Er EISCONN
 108 when trying to establish a connection on a socket which
 109 already has one, or when trying to send a datagram with the destination
 110 address specified and the socket is already connected;
 111 .It Bq Er ENOTCONN
 112 when trying to send a datagram, but
 113 no destination address is specified, and the socket hasn't been
 114 connected;
 115 .It Bq Er ENOBUFS
 116 when the system runs out of memory for
 117 an internal data structure;
 118 .It Bq Er EADDRINUSE
 119 when an attempt
 120 is made to create a socket with a port which has already been
 121 allocated;
 122 .It Bq Er EADDRNOTAVAIL
 123 when an attempt is made to create a
 124 socket with a network address for which no network interface
 125 exists.
 126 .El
 127 .Sh SEE ALSO
 128 .Xr getsockopt 2 ,
 129 .Xr recv 2 ,
 130 .Xr send 2 ,
 131 .Xr socket 2 ,
 132 .Xr intro 4 ,
 133 .Xr inet 4 ,
 134 .Xr ip 4
 135 .Sh HISTORY
 136 The
 137 .Nm
 138 protocol appeared in
 139 .Bx 4.2 .