What is my MacBook's public IP address? I am trying to find out my public IP address for my MacBook Air  It is on Comcast/Xfinity Wifi (my parents had some tech dudes set it up). When I check http://ipecho.net or any other I get 73.170.168.215, but this is the same as on my iPhone 8.

On the contrary, the two devices have different local ip addresses with all the numbers the same except the last one 192.168.40.XXX. Is the public IP address the same thing as the router?
The IP you're seeing (73.170.168.215) is the address your router is exposing to the outside world.  The router is masking you're real address to keep you safe.  

Any device that uses that router to connect to the outside world will be 'seen' as having that same IP.  This is why your Mac and your iPhone appear to have the identical IP's when viewed from outside your network.  The public IP  is the address of that router (I'm trying to keep this simple because networking can get really complicated fast).

Your router is responsible for taking the individual device traffic and routing them to the correct device within your "private" network.    

To use BlockheadsServer correctly with your Mac, it's best if you contact their support to determine the best way to configure it.  You don't want to misconfigure a router because you might accidentally open-up your network to malicious activity.