def add_tunnel(self, tunnel, tunnel_key):
        global tun_id
        vlog.info("adding tunnel %s" % tunnel)
        encap, ip = tunnel.split("/")

        if encap != "vxlan_over_ipv4":
            vlog.warn("unsupported tunnel format %s" % encap)
            return

        tun_id += 1
        tun_name 
 
= "vx" + str(tun_id)

        ovs_vsctl("add-port %s %s -- set Interface %s type=vxlan "
                  "options:key=%s options:remote_ip=%s"
                  % (self.short_name, tun_name, tun_name, tunnel_key, ip))

        for i in range(10):
            port_no = ovs_vsctl("get Interface %s ofport
 
" % tun_name)
            if port_no != "-1":
                break
            elif i == 9:
                vlog.warn("couldn't create tunnel %s" % tunnel)
                ovs_vsctl("del-port %s %s" % (self.short_name, tun_name))
                return

            # Give the system a moment to allocate the port number
            time.sleep(
 
0.5)

        self.tunnels[tunnel] = (port_no, tun_name, ip)

        add_bfd(ip)

        ovs_ofctl("add-flow %s table=0,priority=1000,in_port=%s,"
                  "actions=resubmit(,1)"
                  % (self.short_name, port_no))