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28 .\" @(#)udp.4 8.1 (Berkeley) 6/5/93
36 .Nd Internet User Datagram Protocol
42 .Fn socket AF_INET SOCK_DGRAM 0
45 is a simple, unreliable datagram protocol which is used
48 abstraction for the Internet
51 sockets are connectionless, and are
52 normally used with the
58 call may also be used to fix the destination for future
59 packets (in which case the
67 system calls may be used).
70 address formats are identical to those used by
74 provides a port identifier in addition
75 to the normal Internet address format.
79 space is separate from the
90 packets may be sent (assuming the underlying network supports
91 this) by using a reserved
92 .Dq broadcast address ;
94 is network interface dependent.
98 transport level may be used with
103 socket option may be used at the
109 Only one value is supported for this option:
110 .Tn UDP_ENCAP_ESPINUDP
111 from RFC 3948, defined in
113 .Sh MIB (sysctl) Variables
116 protocol implements a number of variables in the
120 MIB, which can be also read or modified with
122 .Bl -tag -width ".Va log_in_vain"
124 When a datagram is received on a port where there is no socket
125 listening, do not return an ICMP port unreachable message.
126 (Disabled by default.
130 Enable UDP checksums (enabled by default).
132 For all UDP datagrams, to ports on which there is no socket
133 listening, log the connection attempt (disabled by default).
135 Maximum outgoing UDP datagram size
137 Maximum space for incoming UDP datagrams
140 A socket operation may fail with one of the following errors returned:
143 when trying to establish a connection on a socket which
144 already has one, or when trying to send a datagram with the destination
145 address specified and the socket is already connected;
147 when trying to send a datagram, but
148 no destination address is specified, and the socket has not been
151 when the system runs out of memory for
152 an internal data structure;
155 is made to create a socket with a port which has already been
157 .It Bq Er EADDRNOTAVAIL
158 when an attempt is made to create a
159 socket with a network address for which no network interface