[Twisted-Python] sniffing multicast traffic

[Ben Barker]

>> But I seem to have trouble getting them to receive anything at all.
>
> That's a little vague. Does "trouble" mean "it sometimes works" or
> "never works"?
>

Sorry - yes, it was very vague! Never works. If I run wiresahrk I can
see udp packets addressed to 224.0.0.4, port 901, flying past, however
when I run my python script it does not appear to ever receive
anything.

The scritp I am running is almost identical to an exampel I found here:

http://code.activestate.com/recipes/425975-simple-udp-multicast-client-
server-using-twisted/

>>
>> I have managed to use tshark to display the packets :
>>
>> tshark -i eth0  -x -l -f udp
>>
> Can you post a complete example that isn't working for you?
>
> When your code is running, have a look "/sbin/ip maddr" to ensure the
> group has been added to the socket listen filter
eth1
	link  01:00:5e:00:00:04
	link  33:33:ff:7a:7e:4e
	link  01:00:5e:00:00:fb
	link  01:00:5e:00:00:01
	link  33:33:00:00:00:01
	inet  224.0.0.4
	inet  224.0.0.251
	inet  224.0.0.1
	inet6 ff02::1:ff7a:7e4e
	inet6 ff02::1

That's interesting.... eth1 is the wrong interface! In fact, it isn't
connected to anything at all. eth0 is the interface that should be
being used. I will try to swap them around, but presumably this is
something I can specify somwhere...


As I said, the code I am using is taken from the above link, but the
exact listing is given below:

from twisted.internet.protocol import DatagramProtocol
from twisted.internet import reactor
from twisted.application.internet import MulticastServer

class MulticastServerUDP(DatagramProtocol):
    def startProtocol(self):
        print 'Started Listening'
        # Join a specific multicast group, which is the IP we will respond to
        self.transport.joinGroup('224.0.0.4')

    def datagramReceived(self, datagram, address):
            print "Server Received:" + repr(datagram)


reactor.listenMulticast(901, MulticastServerUDP())
reactor.run()



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