xref: /dragonfly/share/man/man4/udp.4 (revision 36a3d1d6) 
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