1.\" Copyright (c) 1983, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)udp.4 8.1 (Berkeley) 6/5/93 33.\" $Id$ 34.\" 35.Dd June 5, 1993 36.Dt UDP 4 37.Os BSD 4.2 38.Sh NAME 39.Nm udp 40.Nd Internet User Datagram Protocol 41.Sh SYNOPSIS 42.Fd #include <sys/socket.h> 43.Fd #include <netinet/in.h> 44.Ft int 45.Fn socket AF_INET 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. Note that the 79.Tn UDP 80port 81space is separate from the 82.Tn TCP 83port space (i.e. a 84.Tn UDP 85port 86may not be 87.Dq connected 88to a 89.Tn TCP 90port). In addition broadcast 91packets may be sent (assuming the underlying network supports 92this) by using a reserved 93.Dq broadcast address ; 94this address 95is network interface dependent. 96.Pp 97Options at the 98.Tn IP 99transport level may be used with 100.Tn UDP ; 101see 102.Xr ip 4 . 103.Sh DIAGNOSTICS 104A socket operation may fail with one of the following errors returned: 105.Bl -tag -width [EADDRNOTAVAIL] 106.It Bq Er EISCONN 107when trying to establish a connection on a socket which 108already has one, or when trying to send a datagram with the destination 109address specified and the socket is already connected; 110.It Bq Er ENOTCONN 111when trying to send a datagram, but 112no destination address is specified, and the socket hasn't been 113connected; 114.It Bq Er ENOBUFS 115when the system runs out of memory for 116an internal data structure; 117.It Bq Er EADDRINUSE 118when an attempt 119is made to create a socket with a port which has already been 120allocated; 121.It Bq Er EADDRNOTAVAIL 122when an attempt is made to create a 123socket with a network address for which no network interface 124exists. 125.El 126.Sh SEE ALSO 127.Xr getsockopt 2 , 128.Xr recv 2 , 129.Xr send 2 , 130.Xr socket 2 , 131.Xr inet 4 , 132.Xr intro 4 , 133.Xr ip 4 134.Sh HISTORY 135The 136.Nm 137protocol appeared in 138.Bx 4.2 . 139