xref: /dragonfly/share/man/man4/udp.4 (revision 984263bc) 
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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 $
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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.  Note that the
80.Tn UDP
81port
82space is separate from the
83.Tn TCP
84port space (i.e. a
85.Tn UDP
86port
87may not be
88.Dq connected
89to a
90.Tn TCP
91port).  In addition broadcast
92packets may be sent (assuming the underlying network supports
93this) by using a reserved
94.Dq broadcast address ;
95this address
96is network interface dependent.
97.Pp
98Options at the
99.Tn IP
100transport level may be used with
101.Tn UDP ;
102see
103.Xr ip 4 .
104.Sh ERRORS
105A socket operation may fail with one of the following errors returned:
106.Bl -tag -width Er
107.It Bq Er EISCONN
108when trying to establish a connection on a socket which
109already has one, or when trying to send a datagram with the destination
110address specified and the socket is already connected;
111.It Bq Er ENOTCONN
112when trying to send a datagram, but
113no destination address is specified, and the socket hasn't been
114connected;
115.It Bq Er ENOBUFS
116when the system runs out of memory for
117an internal data structure;
118.It Bq Er EADDRINUSE
119when an attempt
120is made to create a socket with a port which has already been
121allocated;
122.It Bq Er EADDRNOTAVAIL
123when an attempt is made to create a
124socket with a network address for which no network interface
125exists.
126.El
127.Sh MIB VARIABLES
128The
129.Nm
130protocol implements a number of variables in the
131.Li net.inet
132branch of the
133.Xr sysctl 3
134MIB.
135.Bl -tag -width UDPCTL_RECVSPACEX
136.It UDPCTL_CHECKSUM
137.Pq udp.checksum
138Enable udp checksums (enabled by default).
139.It UDPCTL_MAXDGRAM
140.Pq udp.maxdgram
141Maximum outgoing UDP datagram size
142.It UDPCTL_RECVSPACE
143.Pq udp.recvspace
144Maximum space for incoming UDP datagrams
145.It udp.log_in_vain
146For all udp datagrams, to ports on which there is no socket
147listening, log the connection attempt (disabled by default).
148.It udp.blackhole
149When a datagram is received on a port where there is no socket
150listening, do not return an ICMP port unreachable message.
151(Disabled by default.  See
152.Xr blackhole 4 . )
153.El
154.Sh SEE ALSO
155.Xr getsockopt 2 ,
156.Xr recv 2 ,
157.Xr send 2 ,
158.Xr socket 2 ,
159.Xr blackhole 4 ,
160.Xr inet 4 ,
161.Xr intro 4 ,
162.Xr ip 4
163.Sh HISTORY
164The
165.Nm
166protocol appeared in
167.Bx 4.2 .
168