cf2ca148d9
Add missing sysctls to inet.4 and icmp.4, using references to ip.4 for variables and groups documented there. Add sysctl.8 to "see also" and intro to variable section. Rename "MIB Variables" section to "MIB (sysctl) Variables", as most people will associate with sysctl. Revise history: the ICMP implementation was in 4.2BSD. Reviewed by: manpages(pauamma) Differential Revision: https://reviews.freebsd.org/D36003
177 lines
4.7 KiB
Groff
177 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. 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 August 1, 2022
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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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.Tn UDP_ENCAP
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socket option may be used at the
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.Tn IPPROTO_UDP
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level to encapsulate
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.Tn ESP
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packets in
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.Tn UDP .
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Only one value is supported for this option:
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.Tn UDP_ENCAP_ESPINUDP
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from RFC 3948, defined in
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.In netinet/udp.h .
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.Sh MIB (sysctl) 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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.Va net.inet.udp
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branch of the
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.Xr sysctl 3
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MIB, which can be also read or modified with
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.Xr sysctl 8 :
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.Bl -tag -width ".Va log_in_vain"
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.It Va 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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.It Va checksum
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Enable UDP checksums (enabled by default).
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.It Va 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 Va maxdgram
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Maximum outgoing UDP datagram size
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.It Va recvspace
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Maximum space for incoming UDP datagrams
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.El
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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 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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.Xr udplite 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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