Tunnel.py not working properly on desktops

Hello friends,
I have a petty issue with Gnuradio’s tunnel.py code.I am
running these codes one on a laptop and other on a desktop,with similar
configurations.When I ping from the desktop to the laptop,I am able to
see the ARP packets on my laptop.Also I am able to see the ARP reply
packets.On the laptop I am able to view the successful reception of
packets by the line “RX OK=True”.
However, on the desktop side there is no reception of the reply
ARP packet from the laptop and as a result the ping results in a
‘Destination host unreachable’. Please note that such a error doesnt
arise when using two laptops.
I’ve used the following commands,

Desktop:

  1. sudo python tunnel.py --tx-freq=450M --rx-freq=550M --tx-amplitude=1
    –rx-gain=15 -v

  2. sudo ifconfig gr0 192.168.200.1

Laptop:

1.sudo python tunnel.py --tx-freq=550M --rx-freq=450M --tx-amplitude=1
–rx-gain=15 -v

  1. sudo ifconfig gr0 192.168.200.5

I have also changed the tunnel.py file to send the reply packet after a
delay of 9ms as suggested in some other threads.The following lines have
been changed in tunnel.py

if not payload:
self.tb.send_pkt(eof=True)
break
time.sleep(0.009) # delay 9ms before sending out the reply

t2 = self.tb.source.u.get_time_now().get_real_secs()
print 'reply at time ', t2
if self.verbose:
print “Tx: len(payload) = %4d” % (len(payload),)

However even this has not worked.Hope this issue is sorted out
Thanks in advance!