netdev - Re: H.245v10+ support in nf_conntrack

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Date:	Tue, 1 Sep 2009 14:10:33 +0200
From:	Andreas Jaggi <aj@...n.ch>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Jing Min Zhao <zhaojingmin@...rs.sourceforge.net>,
	netdev@...r.kernel.org
Subject: Re: H.245v10+ support in nf_conntrack_h323?

On Tue, Sep 01, 2009 at 01:25:22PM +0200, Patrick McHardy wrote:
> Mark Brown wrote:
> > I'd be surprised if the H.245 version were the source of your problems
> > here - the new protocol versions are backwards compatible and I don't
> > remember any changes in any of the stuff that's relevant for firewall
> > transit.
> 
> Good point. The helper should also log packets dropped due to parsing
> errors. If you don't get any messages, I'd suggest to use the iptables
> TRACE target to figure out where the packets are dropped exactly.

I'm quite confident that the H.245 parsing/handling is involved in the
packet dropping:
1. there are plenty of 'nf_ct_h245: packet dropped' messages
   (but no nf_ct_q931 or nf_ct_ras messages)
2. without nf_conntrack_h323 the videoconferencing works seamlessly
3. with nf_conntrack_h323 and a ...-j NOTRACK rule the videoconferencing
   works too

In our setup there is a LOG rule preceding any DROP or ACCEPT rule, and
there were no logentries for DROP rules showing up (only the nf_ct_h245:
packet dropped messages).
Would a TRACE rule provide more insight than this? (eg. by showing in
which part of the nf_conntrack_h323 code a packet is dropped?)

For me it looks like nf_conntrack_h323 is not only doing connection
tracking, but also doing protocol enforcement (by dropping packets which
do not correspond exactly to H.245v7).
Perhaps there should be a config option to disable the protocol
enforcement?

Andreas
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