1.\" Copyright (c) 1983, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)udp.4 8.1 (Berkeley) 6/5/93 33.\" $Id: udp.4,v 1.5 1997/02/22 13:24:51 peter Exp $ 34.\" 35.Dd June 5, 1993 36.Dt UDP 4 37.Os BSD 4.2 38.Sh NAME 39.Nm udp 40.Nd Internet User Datagram Protocol 41.Sh SYNOPSIS 42.Fd #include <sys/types.h> 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 49is a simple, unreliable datagram protocol which is used 50to support the 51.Dv SOCK_DGRAM 52abstraction for the Internet 53protocol family. 54.Tn UDP 55sockets are connectionless, and are 56normally used with the 57.Xr sendto 2 58and 59.Xr recvfrom 2 60calls, though the 61.Xr connect 2 62call may also be used to fix the destination for future 63packets (in which case the 64.Xr recv 2 65or 66.Xr read 2 67and 68.Xr send 2 69or 70.Xr write 2 71system calls may be used). 72.Pp 73.Tn UDP 74address formats are identical to those used by 75.Tn TCP . 76In particular 77.Tn UDP 78provides a port identifier in addition 79to the normal Internet address format. Note that the 80.Tn UDP 81port 82space is separate from the 83.Tn TCP 84port space (i.e. a 85.Tn UDP 86port 87may not be 88.Dq connected 89to a 90.Tn TCP 91port). In addition broadcast 92packets may be sent (assuming the underlying network supports 93this) by using a reserved 94.Dq broadcast address ; 95this address 96is network interface dependent. 97.Pp 98Options at the 99.Tn IP 100transport level may be used with 101.Tn UDP ; 102see 103.Xr ip 4 . 104.Sh DIAGNOSTICS 105A socket operation may fail with one of the following errors returned: 106.Bl -tag -width [EADDRNOTAVAIL] 107.It Bq Er EISCONN 108when trying to establish a connection on a socket which 109already has one, or when trying to send a datagram with the destination 110address specified and the socket is already connected; 111.It Bq Er ENOTCONN 112when trying to send a datagram, but 113no destination address is specified, and the socket hasn't been 114connected; 115.It Bq Er ENOBUFS 116when the system runs out of memory for 117an internal data structure; 118.It Bq Er EADDRINUSE 119when an attempt 120is made to create a socket with a port which has already been 121allocated; 122.It Bq Er EADDRNOTAVAIL 123when an attempt is made to create a 124socket with a network address for which no network interface 125exists. 126.El 127.Sh SEE ALSO 128.Xr getsockopt 2 , 129.Xr recv 2 , 130.Xr send 2 , 131.Xr socket 2 , 132.Xr inet 4 , 133.Xr intro 4 , 134.Xr ip 4 135.Sh HISTORY 136The 137.Nm 138protocol appeared in 139.Bx 4.2 . 140