1.\" $OpenBSD: udp.4,v 1.10 2001/11/13 13:54:26 mpech 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. All advertising materials mentioning features or use of this software 16.\" must display the following acknowledgement: 17.\" This product includes software developed by the University of 18.\" California, Berkeley and its contributors. 19.\" 4. Neither the name of the University nor the names of its contributors 20.\" may be used to endorse or promote products derived from this software 21.\" without specific prior written permission. 22.\" 23.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 24.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 26.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 27.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33.\" SUCH DAMAGE. 34.\" 35.\" @(#)udp.4 8.1 (Berkeley) 6/5/93 36.\" 37.Dd June 5, 1993 38.Dt UDP 4 39.Os 40.Sh NAME 41.Nm udp 42.Nd Internet User Datagram Protocol 43.Sh SYNOPSIS 44.Fd #include <sys/socket.h> 45.Fd #include <netinet/in.h> 46.Ft int 47.Fn socket AF_INET SOCK_DGRAM 0 48.Ft int 49.Fn socket AF_INET6 SOCK_DGRAM 0 50.Sh DESCRIPTION 51.Tn UDP 52is a simple, unreliable datagram protocol which is used 53to support the 54.Dv SOCK_DGRAM 55abstraction for the Internet 56protocol family. 57.Tn UDP 58sockets are connectionless, and are 59normally used with the 60.Xr sendto 2 61and 62.Xr recvfrom 2 63calls, though the 64.Xr connect 2 65call may also be used to fix the destination for future 66packets (in which case the 67.Xr recv 2 68or 69.Xr read 2 70and 71.Xr send 2 72or 73.Xr write 2 74system calls may be used). 75.Pp 76.Tn UDP 77address formats are identical to those used by 78.Tn TCP . 79In particular 80.Tn UDP 81provides a port identifier in addition 82to the normal Internet address format. 83Note that the 84.Tn UDP 85port 86space is separate from the 87.Tn TCP 88port space (i.e. a 89.Tn UDP 90port 91may not be 92.Dq connected 93to a 94.Tn TCP 95port). 96In addition broadcast packets may be sent (assuming the underlying network 97supports this) by using a reserved 98.Dq broadcast address ; 99this address 100is network interface dependent. 101.Pp 102Options at the 103.Tn IP 104transport level may be used with 105.Tn UDP ; 106see 107.Xr ip 4 108or 109.Xr ip6 4 . 110.Sh DIAGNOSTICS 111A socket operation may fail with one of the following errors returned: 112.Bl -tag -width [EADDRNOTAVAIL] 113.It Bq Er EISCONN 114when trying to establish a connection on a socket which 115already has one, or when trying to send a datagram with the destination 116address specified and the socket is already connected; 117.It Bq Er ENOTCONN 118when trying to send a datagram, but 119no destination address is specified, and the socket hasn't been 120connected; 121.It Bq Er ENOBUFS 122when the system runs out of memory for 123an internal data structure; 124.It Bq Er EADDRINUSE 125when an attempt 126is made to create a socket with a port which has already been 127allocated; 128.It Bq Er EADDRNOTAVAIL 129when an attempt is made to create a 130socket with a network address for which no network interface 131exists. 132.El 133.Sh SEE ALSO 134.Xr getsockopt 2 , 135.Xr recv 2 , 136.Xr send 2 , 137.Xr socket 2 , 138.Xr inet 4 , 139.Xr inet6 4 , 140.Xr ip 4 , 141.Xr ip6 4 , 142.Xr netintro 4 143.Sh HISTORY 144The 145.Nm 146protocol appeared in 147.Bx 4.2 . 148