On 22/10/2007, at 12:41 AM, Arnaud Bergeron wrote:

quoted text
> 2007/10/21, Damon Schultz <damon@sarahsempire.com>:
>> Greetings,
>>
>> How would one go about routing multicast DNS packets (e.g. used for
>> iTunes sharing neighbourhood discovery) between two different subnets
>> sharing an OpenBSD router and secured by ipsec(4)?
>>
>> So far from multicast(4) I have determined I need to /sbin/sysctl
>> net.inet.ip.mforwarding=1 and I will most likely need to NAT the
>> packets to alter their source address using pf(4) to fool the mDNS
>> client into believing the peers are on the same subnet - but it's
>> what comes inbetween about which I'm not certain.
>>
>> Do I need to employ mrouted(8)?
>>
>> This is my first foray into the bizarre world of IP multicasting...
>> All the HOWTOs I've seen so far describing how to share iTunes
>> libraries across different subnets (e.g. http://wiki.mt-daapd.org/
>> wiki/SSH_Tunnel ) employ an ssh tunnel and a client-side mDNS proxy
>> but I can't help but feel that with a network under my control and
>> OpenBSD routing everything there must be a more elegant solution?
>>
>> Any assistance or advice will be appreciated.
>
> For iTunes sharing you will need a protocol forwarder listening on
> both networks and pasing the traffic.  You don't need this in the
> general case of multicast IP traffic, but iTunes has special provision
> to not share across networks.
>
> For the software to do that, I know Network Beacon but it only works
> on OS X.  You may also be able to use howl (which is in ports) to
> advertise the iTunes shares of one network on the other.

Thanks for your response.

I'm aware that iTunes filters traffic outside of its subnet, I'm  
thinking a pf.conf(5) rule something like

	nat on enc0 inet proto udp from $subnet_A to 224/4 port = 5353 ->  
$subnet_B_gateway static-port

might successfully fool iTunes into not filtering the traffic. This  
wouldn't successfully route the packet, however, as my routing table  
shows

	224/4	127.0.0.1

which I guess means that multicasted traffic needs the assistance of  
mrouted(8) or the like to find its destination. Or could I use the  
route-to option in pf.conf(5) to do this without the complication of  
running a multicast routing daemon, something like

	pass in on enc0 route-to ( enc0 $subnet_B ) inet from $subnet_A to  
224/4

I'll experiment with that a bit, but any assistance in the mean time  
would be appreciated.

Regards,
Damon