The other answers may solve the problem, but there is a "more twisted" (and probably easier) way to listen to a multicast group on multiple interfaces.
Listening to a multicast group on one or more interfaces
To listen to a multicast group on one or more interfaces, provide the IP of each desired interface in multiple calls to the protocol's transport.joinGroup() method as the 'interface' argument.
Below is an example that works on my Linux box, and will make your system listen to multicasts on specific interfaces. Replace the IP addresses with ones belonging to your system.
#!/usr/bin/env python
from twisted.internet import protocol
from twisted.internet import reactor
class MyProtocol(protocol.DatagramProtocol):
def startProtocol(self):
# Join a multicast group, 224.0.0.9, on the interface belonging
# to each of these IPs.
# XXX Replace the interface_ips with one or more IP addresses belonging
# to your system.
for interface_ip in ["192.168.2.2", "10.99.1.100"]:
self.transport.joinGroup("224.0.0.9", interface_ip)
if __name__ == "__main__":
reactor.listenMulticast(1520, MyProtocol())
reactor.run()
You can check that the interface is listening to the new multicast group using the /sbin/ip maddr show command. Find the desired interface name in the command output, and verify that the multicast group shows up beneath it.
The UDP Server example linked in the original post should be able to do the same thing by changing the call to joinGroup() to include the second IP address argument, as above.
Sending multicasts from a particular IP
If you're receiving multicast data on a socket, chances are you will want to send multicast data too -- possibly out of multiple interfaces. Since it's closely related and there are very few examples around I'll throw it in here. Inside a twisted.internet.protocol.DatagramProtocol object you can use the self.transport.setOutgoingInterface() method to control the source IP that will be used for subsequent calls to self.transport.write(). Example showing sending a message from multiple IPs/interfaces:
class MyProtocol(protocol.DatagramProtocol):
# ...
def send_stuff(self, msg):
for src_ip in ["10.0.0.1", "192.168.1.1"]:
self.transport.setOutgoingInterface(src_ip)
self.transport.write(msg, ("224.0.0.9", 1520))
Suppose these IPs were assigned to two different interfaces. Sniffing with Wireshark you would see the message sent out of the first interface, then the second interface, using each IP as a source IP address for the respective transmission.
