1.\" $NetBSD: udp.4,v 1.3 1994/11/30 16:22:41 jtc 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 March 18, 2015 37.Dt UDP 4 38.Os BSD 4.2 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.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 58and 59.Xr recvfrom 60calls, though the 61.Xr connect 2 62or 63.Xr connectx 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. Note that the 82.Tn UDP 83port 84space is separate from the 85.Tn TCP 86port space (i.e. a 87.Tn UDP 88port 89may not be 90.Dq connected 91to a 92.Tn TCP 93port). In addition broadcast 94packets may be sent (assuming the underlying network supports 95this) by using a reserved 96.Dq broadcast address ; 97this address 98is network interface dependent. 99.Pp 100Options at the 101.Tn IP 102transport level may be used with 103.Tn UDP ; 104see 105.Xr ip 4 . 106.Pp 107Using 108.Xr sendmsg 2 109with 110.Dv IP_PKTINFO 111as ancillary data with a non NULL interface index or a local address 112can remove the local IP address that was assigned by a previous call to 113.Xr bind 2 114and leave the UDP socket in an unbound state with 115.Dv INADDR_ANY 116as the local address. 117.Sh DIAGNOSTICS 118A socket operation may fail with one of the following errors returned: 119.Bl -tag -width [EADDRNOTAVAIL] 120.It Bq Er EISCONN 121when trying to establish a connection on a socket which 122already has one, or when trying to send a datagram with the destination 123address specified and the socket is already connected; 124.It Bq Er ENOTCONN 125when trying to send a datagram, but 126no destination address is specified, and the socket hasn't been 127connected; 128.It Bq Er ENOBUFS 129when the system runs out of memory for 130an internal data structure; 131.It Bq Er EADDRINUSE 132when an attempt 133is made to create a socket with a port which has already been 134allocated; 135.It Bq Er EADDRNOTAVAIL 136when an attempt is made to create a 137socket with a network address for which no network interface 138exists. 139.El 140.Sh SEE ALSO 141.Xr bind 2 , 142.Xr connect 2 , 143.Xr connectx 2 , 144.Xr getsockopt 2 , 145.Xr recv 2 , 146.Xr send 2 , 147.Xr sendmsg 2 , 148.Xr socket 2 , 149.Xr inet 4 , 150.Xr intro 4 , 151.Xr ip 4 152.Sh HISTORY 153The 154.Nm 155protocol appeared in 156.Bx 4.2 . 157