1.\" $NetBSD: udp.4,v 1.6 2000/05/22 02:01:34 itojun Exp $ 2.\" 3.\" Copyright (c) 1983, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)udp.4 8.1 (Berkeley) 6/5/93 35.\" 36.Dd June 5, 1993 37.Dt UDP 4 38.Os 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.Ft int 48.Fn socket AF_INET6 SOCK_DGRAM 0 49.Sh DESCRIPTION 50.Tn UDP 51is a simple, unreliable datagram protocol which is used 52to support the 53.Dv SOCK_DGRAM 54abstraction for the Internet 55protocol family. 56.Tn UDP 57sockets are connectionless, and are 58normally used with the 59.Xr sendto 2 60and 61.Xr recvfrom 2 62calls, though the 63.Xr connect 2 64call may also be used to fix the destination for future 65packets (in which case the 66.Xr recv 2 67or 68.Xr read 2 69and 70.Xr send 2 71or 72.Xr write 2 73system calls may be used). 74.Pp 75.Tn UDP 76address formats are identical to those used by 77.Tn TCP . 78In particular 79.Tn UDP 80provides a port identifier in addition 81to the normal Internet address format. 82Note 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). 95In addition broadcast packets may be sent (assuming the underlying 96network supports this) 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 socket with a network address 129for which no network interface exists. 130.El 131.Sh SEE ALSO 132.Xr getsockopt 2 , 133.Xr recv 2 , 134.Xr send 2 , 135.Xr socket 2 , 136.Xr intro 4 , 137.Xr inet 4 , 138.Xr inet6 4 , 139.Xr ip 4 , 140.Xr ip6 4 141.Rs 142.%R RFC 143.%N 768 144.%D August 28, 1980 145.%T "User Datagram Protocol" 146.Re 147.Rs 148.%R RFC 149.%N 1122 150.%D October 1989 151.%T "Requirements for Internet Hosts -- Communication Layers" 152.Re 153.Sh HISTORY 154The 155.Nm 156protocol appeared in 157.Bx 4.2 . 158