'Start NAT/forwarding between Mininet and external network
subnet: Mininet subnet (default 10.0/8)
flush: flush iptables before installing NAT rules'

def __init__(self, name, subnet='10.0/8', localIntf=None, flush=False, **params):

    super(NAT, self).__init__(name, **params)
    self.subnet = subnet
    self.localIntf = localIntf
    self.flush = flush
    self.forwardState = self.cmd('sysctl    -n    net.ipv4.ip_forward').strip()
