netdev - Re: Linux vs FreeBSD Which is correct.

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Date:	Wed, 17 Aug 2011 22:15:52 +0200
From:	Pascal Hambourg <pascal@...uf.fr.eu.org>
To:	sclark46@...thlink.net
CC:	Rémi Denis-Courmont <remi@...lab.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: Linux vs FreeBSD Which is correct.

Hello,

Stephen Clark a écrit :
> On 08/17/2011 01:17 PM, Rémi Denis-Courmont wrote:
>> Le mercredi 17 août 2011 20:03:18 Stephen Clark, vous avez écrit :
>>    
>>> I have run into a situation where if I ping our HQ the response comes
>>> back on a different
>>> interface than what the request went out on. FreeBSD is happy and says
>>> it got the response,
>>> Linux is not and gives no indication it got a response.
>>>
>>> So is FreeBSD wrong or is Linux wrong?

Neither is right or wrong. It partly depends whether you want to enforce
so-called "weak" or "strong" host model.

>> Most distributions enable reverse path filtering by default.
>> It can be disabled:
>> # echo -n 0>  /proc/sys/net/ipv4/conf/all/rp_filter
>>
>> But you should probably fix the configuration instead (e.g. /etc/sysctl.conf).
>>    
> Sorry that didn't help either.

Since some kernel version the logic of this sysctl has changed from
AND(all, $interface) to MAX(all, $interface). So you must set
net/ipv4/conf/$interface/rp_filter to 0 too to disable it.
Or set net/ipv4/conf/all/rp_filter to 2 to make it weaker.
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