cannot access a simple bottle web page in Raspberry Pi from PC

Question

I followed the guide https://bottlepy.org/docs/dev/tutorial.html on Raspberry Pi with the following example

from bottle import route, run
@route('/hello')
def hello():
    return "Hello World!"
run(host='0.0.0.0', port=81, debug=True)

Then I run the python script sudo python hello.py

The web page http://<IP address>:81 is not available, where <IP address> is the IP address of the raspberrry pi.

Running sudo netstat --tcp --udp --listening --program

I obtain

Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name 
tcp   0      0     < IP address >:81        *:*                     LISTEN      26308/python`

Answer 1

iptable is blocking incoming traffic on port 81.

It works after the command sudo iptables -A INPUT -p tcp --dport 81 -j ACCEPT