linux-kernel - Re: /proc/sys/net/ip*/conf/all/* does not actually affect interfaces

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Message-ID: <20090304131333.GA16070@wi-ol.de>
Date:	Wed, 4 Mar 2009 14:13:33 +0100
From:	Philipp Matthias Hahn <pmhahn@...an.lahn.de>
To:	linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: /proc/sys/net/ip*/conf/all/* does not actually affect
	interfaces

Hello Martin!

On Tue, Mar 03, 2009 at 08:27:47PM +0100, martin f krafft wrote:
> also sprach Philipp Matthias Hahn <pmhahn@...an.lahn.de> [2009.03.03.0800 +0100]:

> > Putting a new value in "all" doesn't change the value you read
> > from "$interface", but it only gets computed and used internally.
> 
> Hm, that clears it up... kinda. It does *not* explain by the RAs
> were still accepted (ipv6.conf.all.accept_ra and .autoconf where
> both 0), so unless those values are (wrongly) OR'd, I will need to
> investigate this.

I took another look at
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=include/linux/inetdevice.h;hb=HEAD#l102

102 #define IN_DEV_RX_REDIRECTS(in_dev) \
103         ((IN_DEV_FORWARD(in_dev) && \
104           IN_DEV_ANDCONF((in_dev), ACCEPT_REDIRECTS)) \
105          || (!IN_DEV_FORWARD(in_dev) && \
106           IN_DEV_ORCONF((in_dev), ACCEPT_REDIRECTS)))

"accept_redirect" depends on "forwarding": If forwarding is enabled,
it's ANDed, if it's disabled, it's ORed.

> > "all" on the other hand allways gets applied in addition to the current
> > setting, but it depends on the exact setting, if its ORed, ANDed, or
> > whatevered:
> [...]
> 
> Oh wow. This is very underdocumented.

Yes, I only can agree with you.

BYtE
Phhilipp Hahn
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