URL with Address+Port

1. As mentioned in RFC 5952 Section 6, when you want to specify the port number in a URL, you may type it as "[2001:db8::1]:80".
2. The following three URLs will show the same webpage, because Apache listens on port 80 by default.
   1. http://pearl.csie.ncnu.edu.tw/
   2. http://163.22.22.66/
   3. http://[2001:e10:6840:22:240:f4ff:fee9:14ae]/
   4. http://pearl.csie.ncnu.edu.tw:80/
   5. http://163.22.22.66:80/
   6. http://[2001:e10:6840:22:240:f4ff:fee9:14ae]:80/
3. You may visit a webpage on another port:
   1. http://pearl.csie.ncnu.edu.tw:8006/
   2. http://[2001:e10:6840:22:240:f4ff:fee9:14ae]:8006/
4. If you inspect the packets in Wireshark, they look similar. Please look at the fields of IP addresses and port numbers. Although the URL representation in a browser looks different, they packets they send to the WWW server are the same.
5. PS: I run my Flask script by
   • flask --app my_ip_addr.py run --host '::' --port 8006
   However, this makes it listen to IPv6 only.
   On the contrary, if I run
   • flask --app my_ip_addr.py run --host '' --port 8006
   It listens to IPv4 only.
6. Bonus: Can you find a way to make my Flask program listen to both IPv4/IPv6?