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

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Date:	Tue, 8 Sep 2009 15:04:24 +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?

By using the tcpdumps made during the video conferencing test, I was
able to reproduce the problem with tcpreplay.

Further investigation (eg. sprinkling a couple printks over
nf_conntrack_h323_main.c) showed that the H.245 packet is dropped
because the __nf_ct_expect_check() fails with -EMFILE.
This because max_expected of the H.245 expect policy is reached.

max_expected is set to 'H323_RTP_CHANNEL_MAX * 4 + 2' in
nf_conntrack_h323_main.c and H323_RTP_CHANNEL_MAX is defined as '4'.

Increasing H323_RTP_CHANNEL_MAX solves the problem that H.245 packets
are dropped!

Now I would like to propose a patch to fix this permanently, but I don't
know what a reasonable value for H323_RTP_CHANNEL_MAX would be (only
that the current value is too low for our video conferencing setup).

How was the current value of H323_RTP_CHANNEL_MAX determined? And what
would be the implications of increasing this value?

Andreas
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