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

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Message-ID: <20130816110443.GB5154@breakpoint.cc>
Date:	Fri, 16 Aug 2013 13:04:43 +0200
From:	Florian Westphal <fw@...len.de>
To:	Kristian Evensen <kristian.evensen@...il.com>
Cc:	netfilter@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: MASQUERADE/SNAT and multiple interfaces with the same IP

Kristian Evensen <kristian.evensen@...il.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
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