249 lines
7.1 KiB
Groff
249 lines
7.1 KiB
Groff
.\" $NetBSD: in_getifa.9,v 1.5 2009/03/09 19:24:32 joerg Exp $
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.\"
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.\" Copyright (c) 2006 David Young. All rights reserved.
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.\"
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.\" This code was written by David Young.
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.\"
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.\" Redistribution and use in source and binary forms, with or
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.\" without modification, are permitted provided that the following
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.\" conditions 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
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.\" copyright notice, this list of conditions and the following
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.\" disclaimer in the documentation and/or other materials provided
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.\" with the distribution.
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.\" 3. David Young's name may not be used to endorse or promote
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.\" products derived from this software without specific prior
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.\" written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY DAVID YOUNG ``AS IS'' AND ANY
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.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
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.\" THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
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.\" PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL DAVID
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.\" YOUNG BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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.\" EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
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.\" TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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.\" ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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.\" 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
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.\" OF SUCH DAMAGE.
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.\"
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.Dd February 22, 2007
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.Dt IN_GETIFA 9
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.Os
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.Sh NAME
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.Nm in_getifa
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.Nd Look up the IPv4 source address best matching an IPv4 destination
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.Sh SYNOPSIS
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.Cd options IPSELSRC
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.In netinet/in_selsrc.h
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.Ft struct ifaddr *
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.Fn in_getifa "struct ifaddr *ifa" "const struct sockaddr *dst0"
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.Sh DESCRIPTION
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.Nm
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enforces the IPv4 source-address selection policy.
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Add the source-address selection policy mechanism to your kernel with
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.Cd options IPSELSRC .
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.Cd options IPSELSRC
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lets the operator set the policy for choosing the source address
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of any socket bound to the
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.Dq wildcard
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address,
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.Dv INADDR_ANY .
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Note that the policy is applied
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.Em after
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the kernel makes its forwarding decision, thereby choosing the
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output interface;
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in other words, this mechanism does not affect whether or not
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.Nx
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is a
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.Dq strong ES .
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.Pp
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An operator affects the source-address selection using
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.Xr sysctl 8
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and
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.Xr ifconfig 8 .
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Operators set policies with
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.Xr sysctl 8 .
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Some policies consider the
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.Dq preference number
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of an address.
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An operator may set preference numbers for each address with
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.Xr ifconfig 8 .
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.Pp
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A source-address policy is a priority-ordered list of source-address
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ranking functions.
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A ranking function maps its arguments,
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.Po
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.Em source address ,
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.Em source index ,
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.Em source preference ,
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.Em destination address
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.Pc ,
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to integers.
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The
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.Em source index
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is the position of
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.Em source address
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in the interface address list; the index of the first address is 0.
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The
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.Em source preference
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is the preference number the operator assigned
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to
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.Em source address .
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The
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.Em destination address
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is the socket peer / packet destination.
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.Pp
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Presently, there are four ranking functions to choose from:
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.Bl -tag -width "common-prefix-len"
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.It index
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ranks by
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.Em source index ;
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lower indices are ranked more highly.
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.It preference
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ranks by
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.Em source preference ;
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higher preference numbers are ranked more highly.
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.It common-prefix-len
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ranks each
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.Em source address
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by the length of the longest prefix it has in common with
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.Em destination address ;
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longer common prefixes rank more highly.
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.It same-category
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determines the "categories" of
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.Em source
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and
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.Em destination address .
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A category is one of
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.Em private ,
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.Em link-local ,
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or
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.Em other .
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If the categories exactly match, same-category assigns a rank of 2.
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Some sources are ranked 1 by category:
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a
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.Em link-local
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source with a
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.Em private
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destination, a
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.Em private
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source with a
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.Em link-local
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destination, and a
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.Em private
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source with an
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.Em other
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destination rank 1.
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All other sources rank 0.
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.Pp
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Categories are defined as follows.
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.Bl -tag -width "link-local"
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.It private
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RFC1918 networks, 192.168/16, 172.16/12, and 10/8
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.It link-local
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169.254/16, 224/24
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.It other
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all other networks---i.e., not private, not link-local
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.El
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.El
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.Pp
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To apply a policy, the kernel applies all ranking functions in the policy
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to every source address, producing a vector of ranks for each source.
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The kernel sorts the sources in descending, lexicographical order by their
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rank-vector, and chooses the highest-ranking (first) source.
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The kernel breaks ties by choosing the source with the least
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.Em source index .
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.Pp
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The operator may set a policy on individual interfaces.
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The operator may also set a global policy that applies to all
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interfaces whose policy he does not set individually.
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.Pp
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Here is the sysctl tree for the policy at system startup:
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.Pp
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.Bd -literal -offset indent
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net.inet.ip.selectsrc.default = index
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net.inet.ip.interfaces.ath0.selectsrc =
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net.inet.ip.interfaces.sip0.selectsrc =
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net.inet.ip.interfaces.sip1.selectsrc =
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net.inet.ip.interfaces.lo0.selectsrc =
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net.inet.ip.interfaces.pflog0.selectsrc =
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.Ed
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.Pp
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The policy on every interface is the
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.Dq empty
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policy, so the default policy applies.
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The default policy,
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.Em index ,
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is the
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.Dq historical
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policy in
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.Nx .
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.Pp
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The operator may override the default policy on ath0,
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.Bd -literal -offset indent
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# sysctl -w net.inet.ip.interfaces.ath0.selectsrc=same-category,common-prefix-len,preference
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.Ed
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.Pp
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yielding this policy:
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.Bd -literal -offset indent
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net.inet.ip.selectsrc.default = index
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net.inet.ip.interfaces.ath0.selectsrc = same-category,common-prefix-len,preference
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.Ed
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.Pp
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The operator may set a new default,
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.Bd -literal -offset indent
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# sysctl -w net.inet.ip.selectsrc.debug=\
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\*[Gt] same-category,common-prefix-len,preference
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# sysctl -w net.inet.ip.interfaces.ath0.selectsrc=
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.Ed
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.Pp
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yielding this policy:
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.Bd -literal -offset indent
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net.inet.ip.selectsrc.default = same-category,common-prefix-len,preference
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net.inet.ip.interfaces.ath0.selectsrc =
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.Ed
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.Pp
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In a number of applications, the policy above will usually pick
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suitable source addresses if ath0 is configured in this way:
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.Bd -literal -offset indent
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# ifconfig ath0 inet 64.198.255.1/24
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# ifconfig ath0 inet 10.0.0.1/24
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# ifconfig ath0 inet 169.254.1.1/24
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# ifconfig ath0 inet 192.168.49.1/24 preference 5
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# ifconfig ath0 inet 192.168.37.1/24 preference 9
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.Ed
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A sysctl, net.inet.ip.selectsrc.debug, turns on and off debug messages
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concerned with source selection.
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You may set it to 0 (no messages) or 1.
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.Sh SEE ALSO
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.Xr ifconfig 8 ,
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.Xr sysctl 8
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.Sh STANDARDS
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The family of IPv6 source-address selection policies defined by
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.Li RFC3484
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resembles the family of IPv4 policies that
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.Nm
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enforces.
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.Sh AUTHORS
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.An David Young Aq dyoung@NetBSD.org
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.Sh BUGS
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With
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.Cd options IPSELSRC ,
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a new interface
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.Xr ioctl 2 ,
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.Dv SIOCSIFADDRPREF ,
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was introduced.
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It ought to be documented in
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.Xr inet 4 .
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Also,
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.Xr options 4
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ought to cross-reference this manual page.
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.Pp
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This work should be used to set IPv6 source-address selection
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policies, especially the family of policies defined by
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.Li RFC3484 .
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