bsd/man/man4/udp.4

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  34 .\"     @(#)udp.4       8.1 (Berkeley) 6/5/93
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  36 .Dd March 18, 2015
  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 or
  63 .Xr connectx 2
  64 call may also be used to fix the destination for future
  65 packets (in which case the
  66 .Xr recv 2
  67 or
  68 .Xr read 2
  69 and
  70 .Xr send 2
  71 or
  72 .Xr write 2
  73 system calls may be used).
  74 .Pp
  75 .Tn UDP
  76 address formats are identical to those used by
  77 .Tn TCP .
  78 In particular
  79 .Tn UDP
  80 provides a port identifier in addition
  81 to the normal Internet address format.  Note that the
  82 .Tn UDP
  83 port
  84 space is separate from the
  85 .Tn TCP
  86 port space (i.e. a
  87 .Tn UDP
  88 port
  89 may not be
  90 .Dq connected
  91 to a
  92 .Tn TCP
  93 port).  In addition broadcast
  94 packets may be sent (assuming the underlying network supports
  95 this) by using a reserved
  96 .Dq broadcast address ;
  97 this address
  98 is network interface dependent.
  99 .Pp
 100 Options at the
 101 .Tn IP
 102 transport level may be used with
 103 .Tn UDP ;
 104 see
 105 .Xr ip 4 .
 106 .Sh DIAGNOSTICS
 107 A socket operation may fail with one of the following errors returned:
 108 .Bl -tag -width [EADDRNOTAVAIL]
 109 .It Bq Er EISCONN
 110 when trying to establish a connection on a socket which
 111 already has one, or when trying to send a datagram with the destination
 112 address specified and the socket is already connected;
 113 .It Bq Er ENOTCONN
 114 when trying to send a datagram, but
 115 no destination address is specified, and the socket hasn't been
 116 connected;
 117 .It Bq Er ENOBUFS
 118 when the system runs out of memory for
 119 an internal data structure;
 120 .It Bq Er EADDRINUSE
 121 when an attempt
 122 is made to create a socket with a port which has already been
 123 allocated;
 124 .It Bq Er EADDRNOTAVAIL
 125 when an attempt is made to create a
 126 socket with a network address for which no network interface
 127 exists.
 128 .El
 129 .Sh SEE ALSO
 130 .Xr connect 2 ,
 131 .Xr connectx 2 ,
 132 .Xr getsockopt 2 ,
 133 .Xr recv 2 ,
 134 .Xr send 2 ,
 135 .Xr socket 2 ,
 136 .Xr inet 4 ,
 137 .Xr intro 4 ,
 138 .Xr ip 4
 139 .Sh HISTORY
 140 The
 141 .Nm
 142 protocol appeared in
 143 .Bx 4.2 .