Network with STP can't connect to external VM!

[SalarJamal]

Hi dear,
I am working on a scenario in Mininet-WiFi VM shown in figure bellow, I connected s5 to external Linux VM by adding external interface, but when I make ping form h1 or h2 to the external host it shows "destination host unreachable". h1 and h2 can ping each other successfully. I am running Ryu controller with "simple_switch_stp_13.py".
btw, when I removed link 1 and link 2 and running "simple_switch_13.py" the hosts h1 and h2 can ping the external Linux VM without any problem.
Why a network with STP not connect to external VM?
yours sincerely,

[ramonfontes]

Closing because this is not a mn-wifi book issue