a =     (match(switch=1, dstip=IPAddr('10.0.0.1')) >> fwd(4))
    a = a + (match(switch=1, dstip=IPAddr('10.0.0.2')) >> fwd(5))
    a = a + (match(switch=1, srcip=IPAddr('10.0.0.1'), dstip=IPAddr('10.0.0.3')) >> fwd(1))
    a = a + (match(switch=1, srcip=IPAddr('10.0.0.1'), dstip=IPAddr('10.0.0.4')) >> fwd(1))
    a = a + (match(switch=1, scrip=IPAddr('10.0.0.2'), dstip=IPAddr('10.0.0.3')) >> fwd(3))
    a = a + (match(switch=1, scrip=IPAddr('10.0.0.2'), dstip=IPAddr('10.0.0.4')) >> fwd(3))

    #switch2
    a = a + (match(switch=2, inport=1) >> fwd(2))
    a = a + (match(switch=2, inport=2) >> fwd(1))

    #switch4
    a = a + (match(switch=4, dstip=IPAddr('10.0.0.1')) >> fwd(2))
    a = a + (match(switch=4, dstip=IPAddr('10.0.0.2')) >> fwd(1))
    a = a + (match(switch=4, dstip=IPAddr('10.0.0.3')) >> fwd(4))
    a = a + (match(switch=4, dstip=IPAddr('10.0.0.4')) >> fwd(5))