When I use netstat to list ports, I don't see direct ports such as port 22, port 80, etc... I did see 80 but I also see a bunch of others with really high numbers like... well what is I-node?

From a page from my server provider I am told that by default these are the open ports: 21,22,23,25,53,80,110,143,443,10000 so I guess I don't have to block?

I'm just not sure really. I don't believe that I use SMTP, not yet anyway.

A secondary question is using key-based authentication of port 22, my concern is that I have a dynamic ip-address although I'm not sure if that is relevant. Does the 192. ip address change? Or is it only the public ip such as 72 which is what I see when I type in Google "What is my ip address"

Thanks for any help

Those ports may be "open" upstream from your service provider, but unless you are running services on those ports, they are closed.

What OS. etc... (you know, the usual questions?)

https://www.linuxquestions.org/quest...#faq_lqwelcome

wrt: open ports
to see what's using the port and has it open.

I'm a bit confused. I do not really understand what do you want to know.
ports are usually protected by firewall. Ports are only opened if there is an app listening on it. That means there should be a program waiting for something on that port. Without apps nothing will listen, the ports will be closed. But using a firewall you can restrict if a port available at all.
You cannot set up any authentication on any port but on the listening application. 22 is usually used by sshd.

Your IP address is probably dynamic and depends on your router, but without knowing your config it is only a guess.