netdev - Re: MASQUERADE/SNAT and multiple interfaces with the same IP

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Message-ID: <CAKfDRXgNtPgQjtrSL=oVkws6GB_sTv+h+-_GLVvVvpWoEHBRnw@mail.gmail.com>
Date:	Fri, 16 Aug 2013 13:14:46 +0200
From:	Kristian Evensen <kristian.evensen@...il.com>
To:	Florian Westphal <fw@...len.de>
Cc:	netfilter@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: MASQUERADE/SNAT and multiple interfaces with the same IP

Thank you very much for your reply.

On Fri, Aug 16, 2013 at 1:04 PM, Florian Westphal <fw@...len.de> wrote:>
> The MASQUERADE target zaps conntracks that it "owned" when the
> associated link goes down, see masq_device_event() in ipt_MASQUERADE.c

I added a pr_info() here to see when this function was called. It is
triggered when the link goes down, as expected, but not when I just
change the mark and move the flows to another interface. I still see
the DESTROY/NEW-behavior though.

> Also, the nat core zaps conntracks when they are sent out on an
> interface other than the original interface.
>
> See nf_nat_oif_changed() in iptable_nat.c

Thanks for letting me know, I will start looking into this function.
Does this mean that even when using SNAT, the old mapping is deleted
and a new created? And does this event not notify conntrack? I have so
far used conntrack -E to monitor changes to nat, but that is perhaps
incorrect?

-Kristian
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