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.\" $FreeBSD: src/share/man/man4/udp.4,v 1.8.2.4 2001/12/17 11:30:12 ru Exp $ 34.\" $DragonFly: src/share/man/man4/udp.4,v 1.2 2003/06/17 04:36:59 dillon Exp $ 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.In sys/types.h 44.In sys/socket.h 45.In netinet/in.h 46.Ft int 47.Fn socket AF_INET SOCK_DGRAM 0 48.Sh DESCRIPTION 49.Tn UDP 50is a simple, unreliable datagram protocol which is used 51to support the 52.Dv SOCK_DGRAM 53abstraction for the Internet 54protocol family. 55.Tn UDP 56sockets are connectionless, and are 57normally used with the 58.Xr sendto 2 59and 60.Xr recvfrom 2 61calls, though the 62.Xr connect 2 63call may also be used to fix the destination for future 64packets (in which case the 65.Xr recv 2 66or 67.Xr read 2 68and 69.Xr send 2 70or 71.Xr write 2 72system calls may be used). 73.Pp 74.Tn UDP 75address formats are identical to those used by 76.Tn TCP . 77In particular 78.Tn UDP 79provides a port identifier in addition 80to the normal Internet address format. Note that the 81.Tn UDP 82port 83space is separate from the 84.Tn TCP 85port space (i.e. a 86.Tn UDP 87port 88may not be 89.Dq connected 90to a 91.Tn TCP 92port). In addition broadcast 93packets may be sent (assuming the underlying network supports 94this) by using a reserved 95.Dq broadcast address ; 96this address 97is network interface dependent. 98.Pp 99Options at the 100.Tn IP 101transport level may be used with 102.Tn UDP ; 103see 104.Xr ip 4 . 105.Sh ERRORS 106A socket operation may fail with one of the following errors returned: 107.Bl -tag -width Er 108.It Bq Er EISCONN 109when trying to establish a connection on a socket which 110already has one, or when trying to send a datagram with the destination 111address specified and the socket is already connected; 112.It Bq Er ENOTCONN 113when trying to send a datagram, but 114no destination address is specified, and the socket hasn't been 115connected; 116.It Bq Er ENOBUFS 117when the system runs out of memory for 118an internal data structure; 119.It Bq Er EADDRINUSE 120when an attempt 121is made to create a socket with a port which has already been 122allocated; 123.It Bq Er EADDRNOTAVAIL 124when an attempt is made to create a 125socket with a network address for which no network interface 126exists. 127.El 128.Sh MIB VARIABLES 129The 130.Nm 131protocol implements a number of variables in the 132.Li net.inet 133branch of the 134.Xr sysctl 3 135MIB. 136.Bl -tag -width UDPCTL_RECVSPACEX 137.It UDPCTL_CHECKSUM 138.Pq udp.checksum 139Enable udp checksums (enabled by default). 140.It UDPCTL_MAXDGRAM 141.Pq udp.maxdgram 142Maximum outgoing UDP datagram size 143.It UDPCTL_RECVSPACE 144.Pq udp.recvspace 145Maximum space for incoming UDP datagrams 146.It udp.log_in_vain 147For all udp datagrams, to ports on which there is no socket 148listening, log the connection attempt (disabled by default). 149.It udp.blackhole 150When a datagram is received on a port where there is no socket 151listening, do not return an ICMP port unreachable message. 152(Disabled by default. See 153.Xr blackhole 4 . ) 154.El 155.Sh SEE ALSO 156.Xr getsockopt 2 , 157.Xr recv 2 , 158.Xr send 2 , 159.Xr socket 2 , 160.Xr blackhole 4 , 161.Xr inet 4 , 162.Xr intro 4 , 163.Xr ip 4 164.Sh HISTORY 165The 166.Nm 167protocol appeared in 168.Bx 4.2 . 169