mininetのカスタムトポロジで

from mininet.topo import Topo

class MyTopo( Topo ):
    "Simple topology example."

    def __init__( self ):
        "Create custom topo."

        # Initialize topology
        Topo.__init__( self )

        # Add hosts and switches , controller
        Switch1 = self.addSwitch( 's1', ip='192.168.1.101',　dpid='0000000000000001' )
        Switch2 = self.addSwitch( 's2' , ip='192.168.1.102' , dpid='0000000000000002' )
        Host1 = self.addHost( 'h1' , ip='192.168.1.1' , mac='00:00:00:00:00:01')
        Host2 = self.addHost( 'h2' , ip='192.168.1.2' , mac='00:00:00:00:00:02' )
        Host3 = self.addHost( 'h3' , ip='192.168.1.3' , mac='00:00:00:00:00:03' )

        # Add links
        self.addLink( Switch1, Host1 )
        self.addLink( Switch1, Host2 )
        self.addLink( Switch1, Host3 )
        self.addLink( Switch2, Host1 )
        self.addLink( Switch2, Host2 )
        self.addLink( Switch2, Host3 )

topos = { 'mytopo': ( lambda: MyTopo() ) }

画像の説明をここに入力

このような設定をしました。
switch1のポートを閉じてswitch2を経由してhost同士の疎通を図ろうとしたらうまくいきません。
switch1を経由した疎通確認はとれます。
なぜswitch2ではできないのでしょか？

controllerで実行しているプログラムは以下です。

from ryu.base import app_manager
from ryu.controller import ofp_event
from ryu.controller.handler import CONFIG_DISPATCHER, MAIN_DISPATCHER
from ryu.controller.handler import set_ev_cls
from ryu.ofproto import ofproto_v1_3
from ryu.lib.packet import packet
from ryu.lib.packet import ethernet


class ExampleSwitch13(app_manager.RyuApp):
    OFP_VERSIONS = [ofproto_v1_3.OFP_VERSION]

    def __init__(self, *args, **kwargs):
        super(ExampleSwitch13, self).__init__(*args, **kwargs)
        # initialize mac address table.
        self.mac_to_port = {}

    @set_ev_cls(ofp_event.EventOFPSwitchFeatures, CONFIG_DISPATCHER)
    def switch_features_handler(self, ev):
        datapath = ev.msg.datapath
        ofproto = datapath.ofproto
        parser = datapath.ofproto_parser

        # install the table-miss flow entry.
        match = parser.OFPMatch()
        actions = [parser.OFPActionOutput(ofproto.OFPP_CONTROLLER,
                                          ofproto.OFPCML_NO_BUFFER)]
        self.add_flow(datapath, 0, match, actions)

    def add_flow(self, datapath, priority, match, actions):
        ofproto = datapath.ofproto
        parser = datapath.ofproto_parser

        # construct flow_mod message and send it.
        inst = [parser.OFPInstructionActions(ofproto.OFPIT_APPLY_ACTIONS,
                                         actions)]
        mod = parser.OFPFlowMod(datapath=datapath, priority=priority,
                                match=match, instructions=inst)
        datapath.send_msg(mod)

    @set_ev_cls(ofp_event.EventOFPPacketIn, MAIN_DISPATCHER)
    def _packet_in_handler(self, ev):
        msg = ev.msg
        datapath = msg.datapath
        ofproto = datapath.ofproto
        parser = datapath.ofproto_parser

        # get Datapath ID to identify OpenFlow switches.
        dpid = datapath.id
        self.mac_to_port.setdefault(dpid, {})

        # analyse the received packets using the packet library.
        pkt = packet.Packet(msg.data)
        eth_pkt = pkt.get_protocol(ethernet.ethernet)
        dst = eth_pkt.dst
        src = eth_pkt.src

        # get the received port number from packet_in message.
        in_port = msg.match['in_port']

       self.logger.info("packet in %s %s %s %s", dpid, src, dst, in_port)

        # learn a mac address to avoid FLOOD next time.
        self.mac_to_port[dpid][src] = in_port

        # if the destination mac address is already learned,
        # decide which port to output the packet, otherwise FLOOD.
        if dst in self.mac_to_port[dpid]:
            out_port = self.mac_to_port[dpid][dst]
        else:
            out_port = ofproto.OFPP_FLOOD

        # construct action list.
        actions = [parser.OFPActionOutput(out_port)]

        # install a flow to avoid packet_in next time.
        if out_port != ofproto.OFPP_FLOOD:
            match = parser.OFPMatch(in_port=in_port, eth_dst=dst)
            self.add_flow(datapath, 1, match, actions)

        # construct packet_out message and send it.
        out = parser.OFPPacketOut(datapath=datapath,
                                  buffer_id=ofproto.OFP_NO_BUFFER,
                                  in_port=in_port, actions=actions,
                                  data=msg.data)
        datapath.send_msg(out)