1.\" $OpenBSD: udp.4,v 1.13 2015/09/10 17:55:21 schwarze Exp $ 2.\" $NetBSD: udp.4,v 1.3 1994/11/30 16:22:41 jtc Exp $ 3.\" 4.\" Copyright (c) 1983, 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)udp.4 8.1 (Berkeley) 6/5/93 32.\" 33.Dd $Mdocdate: September 10 2015 $ 34.Dt UDP 4 35.Os 36.Sh NAME 37.Nm udp 38.Nd Internet User Datagram Protocol 39.Sh SYNOPSIS 40.In sys/socket.h 41.In netinet/in.h 42.Ft int 43.Fn socket AF_INET SOCK_DGRAM 0 44.Ft int 45.Fn socket AF_INET6 SOCK_DGRAM 0 46.Sh DESCRIPTION 47.Tn UDP 48is a simple, unreliable datagram protocol which is used 49to support the 50.Dv SOCK_DGRAM 51abstraction for the Internet 52protocol family. 53.Tn UDP 54sockets are connectionless, and are 55normally used with the 56.Xr sendto 2 57and 58.Xr recvfrom 2 59calls, though the 60.Xr connect 2 61call may also be used to fix the destination for future 62packets (in which case the 63.Xr recv 2 64or 65.Xr read 2 66and 67.Xr send 2 68or 69.Xr write 2 70system calls may be used). 71.Pp 72.Tn UDP 73address formats are identical to those used by 74.Tn TCP . 75In particular 76.Tn UDP 77provides a port identifier in addition 78to the normal Internet address format. 79Note 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). 92In addition broadcast packets may be sent (assuming the underlying network 93supports this) 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 104or 105.Xr ip6 4 . 106.Sh DIAGNOSTICS 107A socket operation may fail with one of the following errors returned: 108.Bl -tag -width [EADDRNOTAVAIL] 109.It Bq Er EISCONN 110when trying to establish a connection on a socket which 111already has one, or when trying to send a datagram with the destination 112address specified and the socket is already connected; 113.It Bq Er ENOTCONN 114when trying to send a datagram, but 115no destination address is specified, and the socket hasn't been 116connected; 117.It Bq Er ENOBUFS 118when the system runs out of memory for 119an internal data structure; 120.It Bq Er EADDRINUSE 121when an attempt 122is made to create a socket with a port which has already been 123allocated; 124.It Bq Er EADDRNOTAVAIL 125when an attempt is made to create a 126socket with a network address for which no network interface 127exists. 128.El 129.Sh SEE ALSO 130.Xr getsockopt 2 , 131.Xr recv 2 , 132.Xr send 2 , 133.Xr socket 2 , 134.Xr inet 4 , 135.Xr inet6 4 , 136.Xr ip 4 , 137.Xr ip6 4 , 138.Xr netintro 4 139.Sh HISTORY 140The 141.Nm 142protocol appeared in 143.Bx 4.2 . 144