ZeroMQ PUB/SUB - why won't multiple subscribers work?

I'm using ZeroMQ to facilitate a publish/subscribe environment I'm needing. I'm running a publish server on machine A using Python (using EventLoop), and right now I have one subscriber running in C++ on machine B and a second subscriber running in Python (using EventLoop) on machine C. If machine B subscribes to machine A before machine C does, then B gets subscribed messages and C does not. Furthermore, if I look at the established connections on machine A, there only exists a connection for machine B but not for C. If machine C subscribes to A before B does, then it's the other way around. Here's my publisher code: ``` import zmq from zmq.eventloop import ioloop, zmqstream ioloop.install() context = zmq.Context(1) socket = context.socket(zmq.PUB) publisher = zmqstream.ZMQStream(socket) socket.bind("tcp://*:1337") def publish(): publisher.send_multipart(("heartbeat", "OHAI")) ioloop.PeriodicCallback(publish, 5000).start() ioloop.IOLoop.instance().start() ``` Here's my Python subscriber code: ``` import zmq from zmq.eventloop import ioloop, zmqstream ioloop.install() context = zmq.Context(1) socket = context.socket(zmq.SUB) subscriber = zmqstream.ZMQStream(socket) socket.setsockopt(zmq.SUBSCRIBE, "heartbeat") socket.connect("tcp://pub.local:1337") def subscription(message): print "Message Received: %s" % (message[1]) subscriber.on_recv(subscription) ioloop.IOLoop.instance().start() ``` Why isn't my publisher accepting multiple incoming subscriber sockets? It's probably worth noting that multiple subscribers works fine when running them on machine A, but I don't think it's a firewall issue because I tested subscriber connections from B and C to A with the firewall disabled.