linux-kernel - Re: [PATCH v4] netfilter: nf_conntrack_sip: Handle Cisco 7941/7945 IP phones

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Message-ID: <20130117233539.GA15576@1984>
Date:	Fri, 18 Jan 2013 00:35:39 +0100
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	Kevin Cernekee <cernekee@...il.com>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Patrick McHardy <kaber@...sh.net>,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	"Pekka Savola (ipv6)" <pekkas@...core.fi>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Gabor Juhos <juhosg@...nwrt.org>,
	netfilter-devel@...r.kernel.org, netfilter@...r.kernel.org,
	coreteam@...filter.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH v4] netfilter: nf_conntrack_sip: Handle Cisco 7941/7945
 IP phones

On Mon, Dec 17, 2012 at 08:33:58PM -0800, Kevin Cernekee wrote:
> Most SIP devices use a source port of 5060/udp on SIP requests, so the
> response automatically comes back to port 5060:
> 
>     phone_ip:5060 -> proxy_ip:5060   REGISTER
>     proxy_ip:5060 -> phone_ip:5060   100 Trying
> 
> The newer Cisco IP phones, however, use a randomly chosen high source
> port for the SIP request but expect the response on port 5060:
> 
>     phone_ip:49173 -> proxy_ip:5060  REGISTER
>     proxy_ip:5060 -> phone_ip:5060   100 Trying
> 
> Standard Linux NAT, with or without nf_nat_sip, will send the reply back
> to port 49173, not 5060:
> 
>     phone_ip:49173 -> proxy_ip:5060  REGISTER
>     proxy_ip:5060 -> phone_ip:49173  100 Trying
> 
> But the phone is not listening on 49173, so it will never see the reply.
> 
> This patch modifies nf_*_sip to work around this quirk by extracting
> the SIP response port from the Via: header, iff the source IP in the
> packet header matches the source IP in the SIP request.

Applied, thanks Kevin.
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