.\" $NetBSD: udp.4,v 1.3 1994/11/30 16:22:41 jtc Exp $ .\" .\" Copyright (c) 1983, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the University of .\" California, Berkeley and its contributors. .\" 4. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)udp.4 8.1 (Berkeley) 6/5/93 .\" .Dd June 5, 1993 .Dt UDP 4 .Os BSD 4.2 .Sh NAME .Nm udp .Nd Internet User Datagram Protocol .Sh SYNOPSIS .Fd #include <sys/socket.h> .Fd #include <netinet/in.h> .Ft int .Fn socket AF_INET SOCK_DGRAM 0 .Sh DESCRIPTION .Tn UDP is a simple, unreliable datagram protocol which is used to support the .Dv SOCK_DGRAM abstraction for the Internet protocol family. .Tn UDP sockets are connectionless, and are normally used with the .Xr sendto and .Xr recvfrom calls, though the .Xr connect 2 call may also be used to fix the destination for future packets (in which case the .Xr recv 2 or .Xr read 2 and .Xr send 2 or .Xr write 2 system calls may be used). .Pp .Tn UDP address formats are identical to those used by .Tn TCP . In particular .Tn UDP provides a port identifier in addition to the normal Internet address format. Note that the .Tn UDP port space is separate from the .Tn TCP port space (i.e. a .Tn UDP port may not be .Dq connected to a .Tn TCP port). In addition broadcast packets may be sent (assuming the underlying network supports this) by using a reserved .Dq broadcast address ; this address is network interface dependent. .Pp Options at the .Tn IP transport level may be used with .Tn UDP ; see .Xr ip 4 . .Sh DIAGNOSTICS A socket operation may fail with one of the following errors returned: .Bl -tag -width [EADDRNOTAVAIL] .It Bq Er EISCONN when trying to establish a connection on a socket which already has one, or when trying to send a datagram with the destination address specified and the socket is already connected; .It Bq Er ENOTCONN when trying to send a datagram, but no destination address is specified, and the socket hasn't been connected; .It Bq Er ENOBUFS when the system runs out of memory for an internal data structure; .It Bq Er EADDRINUSE when an attempt is made to create a socket with a port which has already been allocated; .It Bq Er EADDRNOTAVAIL when an attempt is made to create a socket with a network address for which no network interface exists. .El .Sh SEE ALSO .Xr getsockopt 2 , .Xr recv 2 , .Xr send 2 , .Xr socket 2 , .Xr inet 4 , .Xr intro 4 , .Xr ip 4 .Sh HISTORY The .Nm protocol appeared in .Bx 4.2 .