title: (mininet) How to create a topology with two routers and their respective hosts
body: <p>The scenario is composed by two routers connected each other r1-r2 (I found LinuxRouter class in the examples given by Mininet). Connecting 3 hosts to r1, each one belonging to a different subnet, the net ping properly.</p>
  
  <pre><code>class LinuxRouter( Node ):
  
      def config( self, **params ):
          super( LinuxRouter, self).config( **params )
          self.cmd( 'sysctl net.ipv4.ip_forward=1' )
  
      def terminate( self ):
          self.cmd( 'sysctl net.ipv4.ip_forward=0' )
          super( LinuxRouter, self ).terminate()
  
  
  class NetworkTopo( Topo ):
  
      def build( self, **_opts ):
          r1 = self.addNode( 'r1', cls=LinuxRouter, ip='192.168.1.1/24' )
          s1, s2, s3, s4= [ self.addSwitch( s ) for s in ( 's1', 's2', 's3','s4') ]
  
          self.addLink( s1, r1, intfName2='r1-eth1', params2={ 'ip' : '192.168.1.1/24' } )  
          self.addLink( s2, r1, intfName2='r1-eth2', params2={ 'ip' : '172.16.0.1/12' } )
          self.addLink( s3, r1, intfName2='r1-eth3', params2={ 'ip' : '10.0.0.1/8' } )
          self.addLink( s4, r1, intfName2='r1-eth4', params2={ 'ip' : '5.5.5.1/16' } )
  
          h1 = self.addHost( 'h1', ip='192.168.1.100/24', defaultRoute='via 192.168.1.1' )
          h2 = self.addHost( 'h2', ip='172.16.0.100/12', defaultRoute='via 172.16.0.1' )
          h3 = self.addHost( 'h3', ip='10.0.0.100/8', defaultRoute='via 10.0.0.1' )
          r2 = self.addNode( 'r2',cls=LinuxRouter,ip='5.5.5.100/16', defaultRoute='via 5.5.5.1' )
  
          for h, s in [ (h1, s1), (h2, s2), (h3, s3) ]:
              self.addLink( h, s)
          self.addLink(r2,s4)
  
  def run():
      topo = NetworkTopo()
      net = Mininet( topo=topo)
      net.start()
      CLI( net )
      net.stop()
  
  if __name__ == '__main__':
      setLogLevel( 'info' )
      run()
  </code></pre>
  
  <p>If I try to add an host (let's call it h4) to r2 just like I did for the other hosts (adding also a switch, s4, just like r2--s4--h4), it's not able to ping. How can I manage it?</p>