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34 .\" @(#)udp.4 8.1 (Berkeley) 6/5/93
35 .\"
36 .Dd June 5, 1993
37 .Dt UDP 4
38 .Os BSD 4.2
39 .Sh NAME
40 .Nm udp
41 .Nd Internet User Datagram Protocol
42 .Sh SYNOPSIS
43 .Fd #include <sys/socket.h>
44 .Fd #include <netinet/in.h>
45 .Ft int
46 .Fn socket AF_INET SOCK_DGRAM 0
47 .Sh DESCRIPTION
48 .Tn UDP
49 is a simple, unreliable datagram protocol which is used
50 to support the
51 .Dv SOCK_DGRAM
52 abstraction for the Internet
53 protocol family.
54 .Tn UDP
55 sockets are connectionless, and are
56 normally used with the
57 .Xr sendto
58 and
59 .Xr recvfrom
60 calls, though the
61 .Xr connect 2
62 call may also be used to fix the destination for future
63 packets (in which case the
64 .Xr recv 2
65 or
66 .Xr read 2
67 and
68 .Xr send 2
69 or
70 .Xr write 2
71 system calls may be used).
72 .Pp
73 .Tn UDP
74 address formats are identical to those used by
75 .Tn TCP .
76 In particular
77 .Tn UDP
78 provides a port identifier in addition
79 to the normal Internet address format. Note that the
80 .Tn UDP
81 port
82 space is separate from the
83 .Tn TCP
84 port space (i.e. a
85 .Tn UDP
86 port
87 may not be
88 .Dq connected
89 to a
90 .Tn TCP
91 port). In addition broadcast
92 packets may be sent (assuming the underlying network supports
93 this) by using a reserved
94 .Dq broadcast address ;
95 this address
96 is network interface dependent.
97 .Pp
98 Options at the
99 .Tn IP
100 transport level may be used with
101 .Tn UDP ;
102 see
103 .Xr ip 4 .
104 .Sh DIAGNOSTICS
105 A socket operation may fail with one of the following errors returned:
106 .Bl -tag -width [EADDRNOTAVAIL]
107 .It Bq Er EISCONN
108 when trying to establish a connection on a socket which
109 already has one, or when trying to send a datagram with the destination
110 address specified and the socket is already connected;
111 .It Bq Er ENOTCONN
112 when trying to send a datagram, but
113 no destination address is specified, and the socket hasn't been
114 connected;
115 .It Bq Er ENOBUFS
116 when the system runs out of memory for
117 an internal data structure;
118 .It Bq Er EADDRINUSE
119 when an attempt
120 is made to create a socket with a port which has already been
121 allocated;
122 .It Bq Er EADDRNOTAVAIL
123 when an attempt is made to create a
124 socket with a network address for which no network interface
125 exists.
126 .El
127 .Sh SEE ALSO
128 .Xr getsockopt 2 ,
129 .Xr recv 2 ,
130 .Xr send 2 ,
131 .Xr socket 2 ,
132 .Xr intro 4 ,
133 .Xr inet 4 ,
134 .Xr ip 4
135 .Sh HISTORY
136 The
137 .Nm
138 protocol appeared in
139 .Bx 4.2 .