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. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)udp.4 8.1 (Berkeley) 6/5/93 29.\" $FreeBSD$ 30.\" 31.Dd June 5, 1993 32.Dt UDP 4 33.Os 34.Sh NAME 35.Nm udp 36.Nd Internet User Datagram Protocol 37.Sh SYNOPSIS 38.In sys/types.h 39.In sys/socket.h 40.In netinet/in.h 41.Ft int 42.Fn socket AF_INET SOCK_DGRAM 0 43.Sh DESCRIPTION 44.Tn UDP 45is a simple, unreliable datagram protocol which is used 46to support the 47.Dv SOCK_DGRAM 48abstraction for the Internet 49protocol family. 50.Tn UDP 51sockets are connectionless, and are 52normally used with the 53.Xr sendto 2 54and 55.Xr recvfrom 2 56calls, though the 57.Xr connect 2 58call may also be used to fix the destination for future 59packets (in which case the 60.Xr recv 2 61or 62.Xr read 2 63and 64.Xr send 2 65or 66.Xr write 2 67system calls may be used). 68.Pp 69.Tn UDP 70address formats are identical to those used by 71.Tn TCP . 72In particular 73.Tn UDP 74provides a port identifier in addition 75to the normal Internet address format. 76Note that the 77.Tn UDP 78port 79space is separate from the 80.Tn TCP 81port space (i.e., a 82.Tn UDP 83port 84may not be 85.Dq connected 86to a 87.Tn TCP 88port). 89In addition broadcast 90packets may be sent (assuming the underlying network supports 91this) by using a reserved 92.Dq broadcast address ; 93this address 94is network interface dependent. 95.Pp 96Options at the 97.Tn IP 98transport level may be used with 99.Tn UDP ; 100see 101.Xr ip 4 . 102.Sh MIB VARIABLES 103The 104.Nm 105protocol implements a number of variables in the 106.Li net.inet 107branch of the 108.Xr sysctl 3 109MIB. 110.Bl -tag -width UDPCTL_RECVSPACEX 111.It UDPCTL_CHECKSUM 112.Pq udp.checksum 113Enable udp checksums (enabled by default). 114.It UDPCTL_MAXDGRAM 115.Pq udp.maxdgram 116Maximum outgoing UDP datagram size 117.It UDPCTL_RECVSPACE 118.Pq udp.recvspace 119Maximum space for incoming UDP datagrams 120.It udp.log_in_vain 121For all udp datagrams, to ports on which there is no socket 122listening, log the connection attempt (disabled by default). 123.It udp.blackhole 124When a datagram is received on a port where there is no socket 125listening, do not return an ICMP port unreachable message. 126(Disabled by default. 127See 128.Xr blackhole 4 . ) 129.El 130.Sh ERRORS 131A socket operation may fail with one of the following errors returned: 132.Bl -tag -width Er 133.It Bq Er EISCONN 134when trying to establish a connection on a socket which 135already has one, or when trying to send a datagram with the destination 136address specified and the socket is already connected; 137.It Bq Er ENOTCONN 138when trying to send a datagram, but 139no destination address is specified, and the socket has not been 140connected; 141.It Bq Er ENOBUFS 142when the system runs out of memory for 143an internal data structure; 144.It Bq Er EADDRINUSE 145when an attempt 146is made to create a socket with a port which has already been 147allocated; 148.It Bq Er EADDRNOTAVAIL 149when an attempt is made to create a 150socket with a network address for which no network interface 151exists. 152.El 153.Sh SEE ALSO 154.Xr getsockopt 2 , 155.Xr recv 2 , 156.Xr send 2 , 157.Xr socket 2 , 158.Xr blackhole 4 , 159.Xr inet 4 , 160.Xr intro 4 , 161.Xr ip 4 162.Sh HISTORY 163The 164.Nm 165protocol appeared in 166.Bx 4.2 . 167