text: from mininet.topo import Topo
  
  class MyTopology(Topo):
      def __init__(self):
          Topo.__init__(self)
          controller = self.addHost('h1')
          broker = self.addHost('h2')
          plant = self.addHost('h3')
          cSwitch = self.addSwitch('s1')
          bSwitch = self.addSwitch('s2')
          pSwitch = self.addSwitch('s3')
  
          self.addLink(controller, cSwitch)
          self.addLink(cSwitch, bSwitch)
  
  
          self.addLink(plant, pSwitch)
          self.addLink(pSwitch, bSwitch)
  
          self.addLink(bSwitch, broker)
  
  
  topos = {'myTopology' : ( lambda: MyTopology() ) }
  
  import time
  time = time.time()
  h1.cmd('tcpdump -w h1' + str(time) + '.pcap &');
  h2.cmd('tcpdump -w h2' + str(time) + '.pcap &');
  h3.cmd('tcpdump -w h3' + str(time) + '.pcap &');
  