Re: [LARTC] UDP multicast stream and NAT

From: Andy Furniss <andy.furniss@dsl.pipex.com>
To: lartc@vger.kernel.org
Subject: Re: [LARTC] UDP multicast stream and NAT
Date: Mon, 12 Dec 2005 02:08:54 +0000	[thread overview]
Message-ID: <439CDBB6.5070307@dsl.pipex.com> (raw)
In-Reply-To: <20051207221003.32802.qmail@web60924.mail.yahoo.com>

Andy Furniss wrote:
> Gabriel wrote:
> 
>> Hi, my ISP is streaming some local concert using UDP
>> multicasting. I followed the instructions on the site which
>> described how to set VLC in order to view the stream, but
>> it didn't work. I am behind a Linux router/firewall doing
>> NAT. Using google, I quickly found out that the
>> netfilter/conntrack code doesn't support NATing multicast
>> traffic. I thought about bridging the internet facing
>> interface (eth0) and (one of) the internal interfaces (the
>> one my computer is plugged into). This way I could set my
>> IP to be public and no routing/NAT would be done on the
>> Linux box. The only problem is that the box has 2 more NICs
>> in it and there are other people connected to those NICs
>> that need to use that connection (hence need to be NATed).
>>
>> Then I tried thinking about a DMZ-like solution where my
>> box would be in the DMZ, but I can't see that working
>> either because I only have one public IP assigned.
>>
>> Can anyone think of any other way for me to be able to view
>> the stream?
>>
>> Thanks.
>>
> 
> I also don't think the bridging will work.
> 
> AIUI stateless NAT using ip doesn't work with 2.6 kernels so thinking 
> about iptables only.
> 
> Maybe you could get something working with the raw table, you can bypass 
> conntrack with that but then I am not sure if you could dnat it ...
> 
> There is another iptables target ROUTE maybe you could use that. If the 
> LAN PC is running Linux then you could setup a vlan/tunnel/something and 
> ROUTE it down there.
> 
> I would also ask this on the netfilter users list.

Anothe thought - I would tcpdump on the internet interface and check if 
you can see multicast traffic.

If you can then try making a normal dnat rule something like -

iptables -I PREROUTING -t nat -i ppp0 --src 224.0.0.0/4 -j DNAT --to 
192.168.0.3

I don't think my isp does multicast - so I have never tried to get it to 
work and haven't got a clue really :-)

Andy.
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