171 lines
4.7 KiB
Groff
171 lines
4.7 KiB
Groff
.\" Copyright (c) 1983, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)udp.4 8.1 (Berkeley) 6/5/93
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.\" $FreeBSD$
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.\"
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.Dd June 5, 1993
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.Dt UDP 4
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.Os
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.Sh NAME
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.Nm udp
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.Nd Internet User Datagram Protocol
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/socket.h
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.In netinet/in.h
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.Ft int
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.Fn socket AF_INET SOCK_DGRAM 0
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.Sh DESCRIPTION
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.Tn UDP
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is a simple, unreliable datagram protocol which is used
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to support the
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.Dv SOCK_DGRAM
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abstraction for the Internet
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protocol family.
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.Tn UDP
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sockets are connectionless, and are
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normally used with the
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.Xr sendto 2
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and
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.Xr recvfrom 2
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calls, though the
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.Xr connect 2
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call may also be used to fix the destination for future
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packets (in which case the
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.Xr recv 2
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or
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.Xr read 2
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and
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.Xr send 2
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or
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.Xr write 2
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system calls may be used).
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.Pp
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.Tn UDP
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address formats are identical to those used by
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.Tn TCP .
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In particular
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.Tn UDP
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provides a port identifier in addition
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to the normal Internet address format.
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Note that the
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.Tn UDP
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port
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space is separate from the
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.Tn TCP
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port space (i.e., a
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.Tn UDP
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port
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may not be
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.Dq connected
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to a
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.Tn TCP
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port).
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In addition broadcast
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packets may be sent (assuming the underlying network supports
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this) by using a reserved
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.Dq broadcast address ;
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this address
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is network interface dependent.
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.Pp
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Options at the
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.Tn IP
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transport level may be used with
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.Tn UDP ;
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see
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.Xr ip 4 .
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.Sh ERRORS
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A socket operation may fail with one of the following errors returned:
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.Bl -tag -width Er
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.It Bq Er EISCONN
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when trying to establish a connection on a socket which
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already has one, or when trying to send a datagram with the destination
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address specified and the socket is already connected;
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.It Bq Er ENOTCONN
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when trying to send a datagram, but
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no destination address is specified, and the socket has not been
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connected;
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.It Bq Er ENOBUFS
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when the system runs out of memory for
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an internal data structure;
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.It Bq Er EADDRINUSE
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when an attempt
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is made to create a socket with a port which has already been
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allocated;
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.It Bq Er EADDRNOTAVAIL
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when an attempt is made to create a
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socket with a network address for which no network interface
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exists.
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.El
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.Sh MIB VARIABLES
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The
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.Nm
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protocol implements a number of variables in the
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.Li net.inet
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branch of the
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.Xr sysctl 3
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MIB.
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.Bl -tag -width UDPCTL_RECVSPACEX
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.It UDPCTL_CHECKSUM
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.Pq udp.checksum
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Enable udp checksums (enabled by default).
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.It UDPCTL_MAXDGRAM
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.Pq udp.maxdgram
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Maximum outgoing UDP datagram size
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.It UDPCTL_RECVSPACE
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.Pq udp.recvspace
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Maximum space for incoming UDP datagrams
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.It udp.log_in_vain
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For all udp datagrams, to ports on which there is no socket
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listening, log the connection attempt (disabled by default).
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.It udp.blackhole
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When a datagram is received on a port where there is no socket
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listening, do not return an ICMP port unreachable message.
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(Disabled by default.
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See
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.Xr blackhole 4 . )
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.El
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.Sh SEE ALSO
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.Xr getsockopt 2 ,
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.Xr recv 2 ,
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.Xr send 2 ,
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.Xr socket 2 ,
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.Xr blackhole 4 ,
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.Xr inet 4 ,
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.Xr intro 4 ,
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.Xr ip 4
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.Sh HISTORY
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The
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.Nm
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protocol appeared in
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.Bx 4.2 .
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