Iperf stuck in mininet custom topology

Question

I am using mininet on a Vagrant virtual machine that emulates Ubuntu Xenial (my laptop runs Windows 10).

The topology is the following, with remote controller, static ARP and OVS Kernel Switch running in user-space:

h1---s1----s4---h3
     | \  / |
     |  s3  |
     | /  \ |
h2---s2----s5---h4

and I have done it with the following Python script:

from mininet.topo import Topo
from mininet.node import Host

class MyTopo(Topo):
    def __init__(self):
        "Create custom topo."
         Topo.__init__(self)

         leftTopHost = self.addHost('h1')
         leftBottomHost = self.addHost('h2')
         rightTopHost = self.addHost('h3')
         rightBottomHost = self.addHost('h4')
         Switch1 = self.addSwitch('s1')
         Switch2 = self.addSwitch('s2')
         Switch3 = self.addSwitch('s3')
         Switch4 = self.addSwitch('s4')
         Switch5 = self.addSwitch('s5')

         self.addLink(leftTopHost, Switch1)
         self.addLink(Switch1, Switch2)
         self.addLink(Switch1, Switch3)
         self.addLink(Switch1, Switch4)

         self.addLink(leftBottomHost, Switch2)
         self.addLink(Switch2, Switch3)
         self.addLink(Switch2, Switch5)

         self.addLink(Switch3, Switch4)
         self.addLink(Switch3, Switch5)

         self.addLink(rightTopHost, Switch4)
         self.addLink(Switch4, Switch5)

         self.addLink(rightBottomHost, Switch5)

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

The basic idea is an MPLS tunnel between h1 and h4, passing through the switches s1, s4 and s5. I include part of the Ryu app I have developed ('part' because the MPLS match and the subsequent ping h1 h4 works fine); assume the output port numbers are the one in the code

Flow rules in s1:

#path h1->h4
...
match = parser.OFPMatch(in_port=1, eth_type=0x800, ip_proto=6)
actions = [parser.OFPActionOutput(4)]
inst = [parser.OFPInstructionActions(ofproto.OFPIT_APPLY_ACTIONS, actions)]
mod = parser.OFPFlowMod(datapath=datapath, priority=1, match=match, 
                        instructions=inst)
datapath.send_msg(mod)

#path h4->h1    
match = parser.OFPMatch(in_port=4, eth_type=0x800, ip_proto=6)
actions = [parser.OFPActionOutput(1)]
inst = [parser.OFPInstructionActions(ofproto.OFPIT_APPLY_ACTIONS, actions)]
mod = parser.OFPFlowMod(datapath=datapath, priority=1, match=match, 
                        instructions=inst)
datapath.send_msg(mod)

Flow rules in s4:

#path h1->h4
...
match = parser.OFPMatch(in_port=1, eth_type=0x800, ip_proto=6)
actions = [parser.OFPActionOutput(4)]
inst = [parser.OFPInstructionActions(ofproto.OFPIT_APPLY_ACTIONS, actions)]
mod = parser.OFPFlowMod(datapath=datapath, priority=1, match=match, 
                        instructions=inst)
datapath.send_msg(mod)

#path h4->h1
match = parser.OFPMatch(in_port=4, eth_type=0x800, ip_proto=6)
actions = [parser.OFPActionOutput(1)]
inst = [parser.OFPInstructionActions(ofproto.OFPIT_APPLY_ACTIONS, actions)]
mod = parser.OFPFlowMod(datapath=datapath, priority=1, match=match, 
                        instructions=inst)
datapath.send_msg(mod)

Flow rules in s5:

#path h1->h4
...
match = parser.OFPMatch(in_port=3, eth_type=0x800, ip_proto=6)
actions = [parser.OFPActionOutput(4)]
inst = [parser.OFPInstructionActions(ofproto.OFPIT_APPLY_ACTIONS, actions)]
mod = parser.OFPFlowMod(datapath=datapath, priority=1, match=match, 
                        instructions=inst)
datapath.send_msg(mod)

#path h4->h1
match = parser.OFPMatch(in_port=4, eth_type=0x800, ip_proto=6)
actions = [parser.OFPActionOutput(3)]
inst = [parser.OFPInstructionActions(ofproto.OFPIT_APPLY_ACTIONS, actions)]
mod = parser.OFPFlowMod(datapath=datapath, priority=1, match=match, 
                        instructions=inst)
datapath.send_msg(mod)

So getting to my issue: I want to generate TCP traffic between h1 and h4 but I can't understand why, when I type the iperf h1 h4 command in the mininet prompt, it results in a connection timeout; same result if I run both the client and the server on separate terminals.

For sure I know I must add something to my code, but I can't really see where.. Any help would be much appreciated!