From mboxrd@z Thu Jan  1 00:00:00 1970
From: Florian Westphal <fw@strlen.de>
Subject: Re: MASQUERADE/SNAT and multiple interfaces with the same IP
Date: Fri, 16 Aug 2013 13:04:43 +0200
Message-ID: <20130816110443.GB5154@breakpoint.cc>
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To: Kristian Evensen <kristian.evensen@gmail.com>
Cc: netfilter@vger.kernel.org, netdev@vger.kernel.org

Kristian Evensen <kristian.evensen@gmail.com> wrote:
> After spending long time looking at the source code, I can't figure
> out why this happens. Once the MASQUERADE/SNAT rule has been inserted,
> to me everything looks the same.

The MASQUERADE target zaps conntracks that it "owned" when the
associated link goes down, see masq_device_event() in ipt_MASQUERADE.c

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