1.\" $OpenBSD: udp.4,v 1.8 2000/12/21 21:01:21 aaron 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 61and 62.Xr recvfrom 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. Note that the 83.Tn UDP 84port 85space is separate from the 86.Tn TCP 87port space (i.e. a 88.Tn UDP 89port 90may not be 91.Dq connected 92to a 93.Tn TCP 94port). In addition broadcast 95packets may be sent (assuming the underlying network supports 96this) by using a reserved 97.Dq broadcast address ; 98this address 99is network interface dependent. 100.Pp 101Options at the 102.Tn IP 103transport level may be used with 104.Tn UDP ; 105see 106.Xr ip 4 107or 108.Xr ip6 4 . 109.Sh DIAGNOSTICS 110A socket operation may fail with one of the following errors returned: 111.Bl -tag -width [EADDRNOTAVAIL] 112.It Bq Er EISCONN 113when trying to establish a connection on a socket which 114already has one, or when trying to send a datagram with the destination 115address specified and the socket is already connected; 116.It Bq Er ENOTCONN 117when trying to send a datagram, but 118no destination address is specified, and the socket hasn't been 119connected; 120.It Bq Er ENOBUFS 121when the system runs out of memory for 122an internal data structure; 123.It Bq Er EADDRINUSE 124when an attempt 125is made to create a socket with a port which has already been 126allocated; 127.It Bq Er EADDRNOTAVAIL 128when an attempt is made to create a 129socket with a network address for which no network interface 130exists. 131.El 132.Sh SEE ALSO 133.Xr getsockopt 2 , 134.Xr recv 2 , 135.Xr send 2 , 136.Xr socket 2 , 137.Xr inet 4 , 138.Xr inet6 4 , 139.Xr ip 4 , 140.Xr ip6 4 , 141.Xr netintro 4 142.Sh HISTORY 143The 144.Nm 145protocol appeared in 146.Bx 4.2 . 147