461 lines
13 KiB
Groff
461 lines
13 KiB
Groff
.\" $KAME: inet6.4,v 1.21 2001/04/05 01:00:18 itojun Exp $
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.\"
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.\" Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
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.\" 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 project 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 PROJECT 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 PROJECT 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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.\" $FreeBSD$
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.\"
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.Dd November 25, 2020
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.Dt INET6 4
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.Os
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.Sh NAME
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.Nm inet6
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.Nd Internet protocol version 6 family
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.Sh SYNOPSIS
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.In sys/types.h
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.In netinet/in.h
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.Sh DESCRIPTION
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The
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.Nm
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family is an updated version of
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.Xr inet 4
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family.
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While
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.Xr inet 4
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implements Internet Protocol version 4,
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.Nm
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implements Internet Protocol version 6.
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.Pp
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.Nm
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is a collection of protocols layered atop the
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.Em Internet Protocol version 6
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.Pq Tn IPv6
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transport layer, and utilizing the IPv6 address format.
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The
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.Nm
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family provides protocol support for the
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.Dv SOCK_STREAM , SOCK_DGRAM ,
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and
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.Dv SOCK_RAW
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socket types; the
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.Dv SOCK_RAW
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interface provides access to the
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.Tn IPv6
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protocol.
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.Sh ADDRESSING
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IPv6 addresses are 16 byte quantities, stored in network standard byteorder.
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The include file
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.In netinet/in.h
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defines this address
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as a discriminated union.
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.Pp
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Sockets bound to the
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.Nm
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family utilize the following addressing structure:
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.Bd -literal -offset indent
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struct sockaddr_in6 {
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uint8_t sin6_len;
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sa_family_t sin6_family;
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in_port_t sin6_port;
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uint32_t sin6_flowinfo;
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struct in6_addr sin6_addr;
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uint32_t sin6_scope_id;
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};
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.Ed
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.Pp
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Sockets may be created with the local address
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.Dq Dv ::
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(which is equal to IPv6 address
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.Dv 0:0:0:0:0:0:0:0 )
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to affect
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.Dq wildcard
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matching on incoming messages.
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.Pp
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The IPv6 specification defines scoped addresses,
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like link-local or site-local addresses.
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A scoped address is ambiguous to the kernel,
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if it is specified without a scope identifier.
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To manipulate scoped addresses properly from the userland,
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programs must use the advanced API defined in RFC2292.
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A compact description of the advanced API is available in
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.Xr ip6 4 .
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If a scoped address is specified without an explicit scope,
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the kernel may raise an error.
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Note that scoped addresses are not for daily use at this moment,
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both from a specification and an implementation point of view.
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.Pp
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The KAME implementation supports an extended numeric IPv6 address notation
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for link-local addresses,
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like
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.Dq Li fe80::1%de0
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to specify
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.Do
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.Li fe80::1
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on
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.Li de0
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interface
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.Dc .
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This notation is supported by
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.Xr getaddrinfo 3
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and
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.Xr getnameinfo 3 .
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Some of normal userland programs, such as
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.Xr telnet 1
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or
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.Xr ftp 1 ,
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are able to use this notation.
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With special programs
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like
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.Xr ping 8 ,
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you can specify the outgoing interface by an extra command line option
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to disambiguate scoped addresses.
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.Pp
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Scoped addresses are handled specially in the kernel.
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In kernel structures like routing tables or interface structures,
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a scoped address will have its interface index embedded into the address.
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Therefore,
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the address in some kernel structures is not the same as that on the wire.
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The embedded index will become visible through a
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.Dv PF_ROUTE
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socket, kernel memory accesses via
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.Xr kvm 3
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and on some other occasions.
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HOWEVER, users should never use the embedded form.
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For details please consult
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.Pa IMPLEMENTATION
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supplied with KAME kit.
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.Sh PROTOCOLS
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The
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.Nm
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family is comprised of the
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.Tn IPv6
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network protocol, Internet Control
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Message Protocol version 6
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.Pq Tn ICMPv6 ,
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Transmission Control Protocol
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.Pq Tn TCP ,
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and User Datagram Protocol
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.Pq Tn UDP .
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.Tn TCP
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is used to support the
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.Dv SOCK_STREAM
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abstraction while
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.Tn UDP
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is used to support the
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.Dv SOCK_DGRAM
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abstraction.
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Note that
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.Tn TCP
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and
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.Tn UDP
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are common to
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.Xr inet 4
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and
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.Nm .
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A raw interface to
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.Tn IPv6
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is available
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by creating an Internet socket of type
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.Dv SOCK_RAW .
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The
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.Tn ICMPv6
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message protocol is accessible from a raw socket.
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.Ss MIB Variables
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A number of variables are implemented in the net.inet6 branch of the
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.Xr sysctl 3
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MIB.
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In addition to the variables supported by the transport protocols
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(for which the respective manual pages may be consulted),
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the following general variables are defined:
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.Bl -tag -width IPV6CTL_MAXFRAGPACKETS
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.It Dv IPV6CTL_FORWARDING
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.Pq ip6.forwarding
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Boolean: enable/disable forwarding of
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.Tn IPv6
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packets.
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Also, identify if the node is acting as a router.
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Defaults to off.
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.It Dv IPV6CTL_SENDREDIRECTS
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.Pq ip6.redirect
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Boolean: enable/disable sending of
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.Tn ICMPv6
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redirects in response to unforwardable
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.Tn IPv6
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packets.
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This option is ignored unless the node is routing
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.Tn IPv6
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packets,
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and should normally be enabled on all systems.
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Defaults to on.
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.It Dv IPV6CTL_DEFHLIM
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.Pq ip6.hlim
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Integer: default hop limit value to use for outgoing
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.Tn IPv6
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packets.
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This value applies to all the transport protocols on top of
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.Tn IPv6 .
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There are APIs to override the value.
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.It Dv IPV6CTL_MAXFRAGS
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.Pq ip6.maxfrags
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Integer: maximum number of fragments the host will accept and simultaneously
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hold across all reassembly queues in all VNETs.
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If set to 0, fragment reassembly is disabled.
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If set to -1, this limit is not applied.
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This limit is recalculated when the number of mbuf clusters is changed.
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This is a global limit.
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.It Dv IPV6CTL_MAXFRAGPACKETS
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.Pq ip6.maxfragpackets
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Integer: maximum number of fragmented packets the node will accept and
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simultaneously hold in the reassembly queue for a particular VNET.
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0 means that the node will not accept any fragmented packets for that VNET.
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-1 means that the node will not apply this limit for that VNET.
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This limit is recalculated when the number of mbuf clusters is changed.
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This is a per-VNET limit.
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.It Dv IPV6CTL_MAXFRAGBUCKETSIZE
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.Pq ip6.maxfragbucketsize
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Integer: maximum number of reassembly queues per bucket.
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Fragmented packets are hashed to buckets.
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Each bucket has a list of reassembly queues.
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The system must compare the incoming packets to the existing reassembly queues
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in the bucket to find a matching reassembly queue.
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To preserve system resources, the system limits the number of reassembly
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queues allowed in each bucket.
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This limit is recalculated when the number of mbuf clusters is changed or
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when the value of
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.Va ip6.maxfragpackets
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changes.
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This is a per-VNET limit.
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.It Dv IPV6CTL_MAXFRAGSPERPACKET
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.Pq ip6.maxfragsperpacket
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Integer: maximum number of fragments the host will accept and hold in the
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ressembly queue for a packet.
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This is a per-VNET limit.
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.It Dv IPV6CTL_ACCEPT_RTADV
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.Pq ip6.accept_rtadv
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Boolean: the default value of a per-interface flag to
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enable/disable receiving of
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.Tn ICMPv6
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router advertisement packets,
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and autoconfiguration of address prefixes and default routers.
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The node must be a host
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(not a router)
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for the option to be meaningful.
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Defaults to off.
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.It Dv IPV6CTL_AUTO_LINKLOCAL
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.Pq ip6.auto_linklocal
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Boolean: the default value of a per-interface flag to
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enable/disable performing automatic link-local address configuration.
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Defaults to on.
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.It Dv IPV6CTL_LOG_INTERVAL
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.Pq ip6.log_interval
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Integer: default interval between
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.Tn IPv6
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packet forwarding engine log output
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(in seconds).
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.It Dv IPV6CTL_HDRNESTLIMIT
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.Pq ip6.hdrnestlimit
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Integer: default number of the maximum
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.Tn IPv6
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extension headers
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permitted on incoming
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.Tn IPv6
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packets.
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If set to 0, the node will accept as many extension headers as possible.
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.It Dv IPV6CTL_DAD_COUNT
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.Pq ip6.dad_count
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Integer: default number of
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.Tn IPv6
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DAD
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.Pq duplicated address detection
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probe packets.
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The packets will be generated when
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.Tn IPv6
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interface addresses are configured.
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.It Dv IPV6CTL_AUTO_FLOWLABEL
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.Pq ip6.auto_flowlabel
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Boolean: enable/disable automatic filling of
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.Tn IPv6
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flowlabel field, for outstanding connected transport protocol packets.
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The field might be used by intermediate routers to identify packet flows.
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Defaults to on.
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.It Dv IPV6CTL_DEFMCASTHLIM
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.Pq ip6.defmcasthlim
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Integer: default hop limit value for an
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.Tn IPv6
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multicast packet sourced by the node.
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This value applies to all the transport protocols on top of
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.Tn IPv6 .
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There are APIs to override the value as documented in
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.Xr ip6 4 .
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.It Dv IPV6CTL_GIF_HLIM
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.Pq ip6.gifhlim
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Integer: default maximum hop limit value for an
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.Tn IPv6
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packet generated by
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.Xr gif 4
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tunnel interface.
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.It Dv IPV6CTL_KAME_VERSION
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.Pq ip6.kame_version
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String: identifies the version of KAME
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.Tn IPv6
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stack implemented in the kernel.
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.It Dv IPV6CTL_USE_DEPRECATED
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.Pq ip6.use_deprecated
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Boolean: enable/disable use of deprecated address,
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specified in RFC2462 5.5.4.
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Defaults to on.
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.It Dv IPV6CTL_RR_PRUNE
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.Pq ip6.rr_prune
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Integer: default interval between
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.Tn IPv6
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router renumbering prefix babysitting, in seconds.
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.It Dv IPV6CTL_V6ONLY
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.Pq ip6.v6only
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Boolean: enable/disable the prohibited use of
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.Tn IPv4
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mapped address on
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.Dv AF_INET6
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sockets.
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Defaults to on.
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.El
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.Ss Interaction between IPv4/v6 sockets
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By default,
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.Fx
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does not route IPv4 traffic to
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.Dv AF_INET6
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sockets.
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The default behavior intentionally violates RFC2553 for security reasons.
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Listen to two sockets if you want to accept both IPv4 and IPv6 traffic.
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IPv4 traffic may be routed with certain
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per-socket/per-node configuration, however, it is not recommended to do so.
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Consult
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.Xr ip6 4
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for details.
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.Pp
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The behavior of
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.Dv AF_INET6
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TCP/UDP socket is documented in RFC2553.
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Basically, it says this:
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.Bl -bullet -compact
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.It
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A specific bind on an
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.Dv AF_INET6
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socket
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.Xr ( bind 2
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with an address specified)
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should accept IPv6 traffic to that address only.
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.It
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If you perform a wildcard bind
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on an
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.Dv AF_INET6
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socket
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.Xr ( bind 2
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to IPv6 address
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.Li :: ) ,
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and there is no wildcard bind
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.Dv AF_INET
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socket on that TCP/UDP port, IPv6 traffic as well as IPv4 traffic
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should be routed to that
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.Dv AF_INET6
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socket.
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IPv4 traffic should be seen as if it came from an IPv6 address like
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.Li ::ffff:10.1.1.1 .
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This is called an IPv4 mapped address.
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.It
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If there are both a wildcard bind
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.Dv AF_INET
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socket and a wildcard bind
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.Dv AF_INET6
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socket on one TCP/UDP port, they should behave separately.
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IPv4 traffic should be routed to the
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.Dv AF_INET
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socket and IPv6 should be routed to the
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.Dv AF_INET6
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socket.
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.El
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.Pp
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However, RFC2553 does not define the ordering constraint between calls to
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.Xr bind 2 ,
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nor how IPv4 TCP/UDP port numbers and IPv6 TCP/UDP port numbers
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relate to each other
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(should they be integrated or separated).
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Implemented behavior is very different from kernel to kernel.
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Therefore, it is unwise to rely too much upon the behavior of
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.Dv AF_INET6
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wildcard bind sockets.
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It is recommended to listen to two sockets, one for
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.Dv AF_INET
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and another for
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.Dv AF_INET6 ,
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when you would like to accept both IPv4 and IPv6 traffic.
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.Pp
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It should also be noted that
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malicious parties can take advantage of the complexity presented above,
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and are able to bypass access control,
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if the target node routes IPv4 traffic to
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.Dv AF_INET6
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socket.
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Users are advised to take care handling connections
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from IPv4 mapped address to
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.Dv AF_INET6
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sockets.
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.Sh SEE ALSO
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.Xr ioctl 2 ,
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.Xr socket 2 ,
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.Xr sysctl 3 ,
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.Xr icmp6 4 ,
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.Xr intro 4 ,
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.Xr ip6 4 ,
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.Xr tcp 4 ,
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.Xr udp 4
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.Sh STANDARDS
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.Rs
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.%A Tatsuya Jinmei
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.%A Atsushi Onoe
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.%T "An Extension of Format for IPv6 Scoped Addresses"
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.%R internet draft
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.%D June 2000
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.%N draft-ietf-ipngwg-scopedaddr-format-02.txt
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.%O work in progress material
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.Re
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.Sh HISTORY
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The
|
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.Nm
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protocol interfaces are defined in RFC2553 and RFC2292.
|
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The implementation described herein appeared in the WIDE/KAME project.
|
|
.Sh BUGS
|
|
The IPv6 support is subject to change as the Internet protocols develop.
|
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Users should not depend on details of the current implementation,
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|
but rather the services exported.
|
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.Pp
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Users are suggested to implement
|
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.Dq version independent
|
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code as much as possible, as you will need to support both
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.Xr inet 4
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and
|
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.Nm .
|