Well, you can check to see if a specific port is open. It's not even all that difficult and it works locally and remotely. You can even check to see if a website has a specific port open and, if the server responds, you'll know if it is open or closed.
Let's say you've changed the port SSH uses and you want to make sure the new port is open, you can do that! You can do quite a bit with this.
linux-tips.us
You might want to keep reading past the 'closure' bit. I just kept on typing! The article is a bit longer than some, but not too long. I do love me some feedback.
Let's say you've changed the port SSH uses and you want to make sure the new port is open, you can do that! You can do quite a bit with this.

How To: Check If A Specific Port Is Open • Linux Tips
In today's article, we're going to learn how to check if a specific port is open. The command is simple, but versatile.

You might want to keep reading past the 'closure' bit. I just kept on typing! The article is a bit longer than some, but not too long. I do love me some feedback.