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.\" $FreeBSD$ 34.\" 35.Dd June 5, 1993 36.Dt UDP 4 37.Os 38.Sh NAME 39.Nm udp 40.Nd Internet User Datagram Protocol 41.Sh SYNOPSIS 42.In sys/types.h 43.In sys/socket.h 44.In 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 2 58and 59.Xr recvfrom 2 60calls, though the 61.Xr connect 2 62call may also be used to fix the destination for future 63packets (in which case the 64.Xr recv 2 65or 66.Xr read 2 67and 68.Xr send 2 69or 70.Xr write 2 71system calls may be used). 72.Pp 73.Tn UDP 74address formats are identical to those used by 75.Tn TCP . 76In particular 77.Tn UDP 78provides a port identifier in addition 79to the normal Internet address format. 80Note 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). 93In 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.Sh ERRORS 107A socket operation may fail with one of the following errors returned: 108.Bl -tag -width Er 109.It Bq Er EISCONN 110when trying to establish a connection on a socket which 111already has one, or when trying to send a datagram with the destination 112address specified and the socket is already connected; 113.It Bq Er ENOTCONN 114when trying to send a datagram, but 115no destination address is specified, and the socket has not been 116connected; 117.It Bq Er ENOBUFS 118when the system runs out of memory for 119an internal data structure; 120.It Bq Er EADDRINUSE 121when an attempt 122is made to create a socket with a port which has already been 123allocated; 124.It Bq Er EADDRNOTAVAIL 125when an attempt is made to create a 126socket with a network address for which no network interface 127exists. 128.El 129.Sh MIB VARIABLES 130The 131.Nm 132protocol implements a number of variables in the 133.Li net.inet 134branch of the 135.Xr sysctl 3 136MIB. 137.Bl -tag -width UDPCTL_RECVSPACEX 138.It UDPCTL_CHECKSUM 139.Pq udp.checksum 140Enable udp checksums (enabled by default). 141.It UDPCTL_MAXDGRAM 142.Pq udp.maxdgram 143Maximum outgoing UDP datagram size 144.It UDPCTL_RECVSPACE 145.Pq udp.recvspace 146Maximum space for incoming UDP datagrams 147.It udp.log_in_vain 148For all udp datagrams, to ports on which there is no socket 149listening, log the connection attempt (disabled by default). 150.It udp.blackhole 151When a datagram is received on a port where there is no socket 152listening, do not return an ICMP port unreachable message. 153(Disabled by default. 154See 155.Xr blackhole 4 . ) 156.El 157.Sh SEE ALSO 158.Xr getsockopt 2 , 159.Xr recv 2 , 160.Xr send 2 , 161.Xr socket 2 , 162.Xr blackhole 4 , 163.Xr inet 4 , 164.Xr intro 4 , 165.Xr ip 4 166.Sh HISTORY 167The 168.Nm 169protocol appeared in 170.Bx 4.2 . 171