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28 .\" @(#)udp.4 8.1 (Berkeley) 6/5/93
29 .\" $FreeBSD: src/share/man/man4/udp.4,v 1.8.2.4 2001/12/17 11:30:12 ru Exp $
30 .\" $DragonFly: src/share/man/man4/udp.4,v 1.2 2003/06/17 04:36:59 dillon Exp $
37 .Nd Internet User Datagram Protocol
43 .Fn socket AF_INET SOCK_DGRAM 0
46 is a simple, unreliable datagram protocol which is used
49 abstraction for the Internet
52 sockets are connectionless, and are
53 normally used with the
59 call may also be used to fix the destination for future
60 packets (in which case the
68 system calls may be used).
71 address formats are identical to those used by
75 provides a port identifier in addition
76 to the normal Internet address format. Note that the
79 space is separate from the
88 port). In addition broadcast
89 packets may be sent (assuming the underlying network supports
90 this) by using a reserved
91 .Dq broadcast address ;
93 is network interface dependent.
97 transport level may be used with
102 A socket operation may fail with one of the following errors returned:
105 when trying to establish a connection on a socket which
106 already has one, or when trying to send a datagram with the destination
107 address specified and the socket is already connected;
109 when trying to send a datagram, but
110 no destination address is specified, and the socket hasn't been
113 when the system runs out of memory for
114 an internal data structure;
117 is made to create a socket with a port which has already been
119 .It Bq Er EADDRNOTAVAIL
120 when an attempt is made to create a
121 socket with a network address for which no network interface
127 protocol implements a number of variables in the
132 .Bl -tag -width UDPCTL_RECVSPACEX
135 Enable udp checksums (enabled by default).
138 Maximum outgoing UDP datagram size
141 Maximum space for incoming UDP datagrams
143 For all udp datagrams, to ports on which there is no socket
144 listening, log the connection attempt (disabled by default).
146 When a datagram is received on a port where there is no socket
147 listening, do not return an ICMP port unreachable message.
148 (Disabled by default. See