netdev - Re: [PATCH/RFC 01/10] Implement local diversion of IPv4 skbs

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Date:	Wed, 10 Jan 2007 13:32:24 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Balazs Scheidler <bazsi@...abit.hu>
CC:	netdev@...r.kernel.org, netfilter-devel@...ts.netfilter.org,
	KOVACS Krisztian <hidden@...abit.hu>
Subject: Re: [PATCH/RFC 01/10] Implement local diversion of IPv4 skbs

Balazs Scheidler wrote:
> On Wed, 2007-01-10 at 07:46 +0100, Patrick McHardy wrote:
> 
>>I'm wondering if it would be possible to use normal input routing
>>combined with netfilter marks to do the diversion ..
>
> 
> The problem is that userspace proxies open ports dynamically (think of
> FTP data channels), you cannot add iptables rule for every such
> redirection. So one rule for every dynamic redirection is a no-go.
> 
> If we'd add a single rule, which would do some kind of lookup and then
> mark packets, would again introduce a state inside tproxy that'd need to
> be synchronized with the socket table. We explicitly wanted to avoid
> such tables.

How exactly are dynamic ports handled? Do you just add a catch-all rule
that filters based on socket lookups?

In that case you could do something like this:

ip route add local default dev lo scope host table 1
ip rule add fwmark 0x1 lookup 1

and still use the socket lookups for marking, which would (without the
socket caching) remove the need for this patch entirely.

> And additionally, using the mark this way would prevent the admin to use
> it they way he/she likes. 

We support bitwise use of the mark everywhere in current kernels, so
that shouldn't be a problem anymore.
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