To find out what your ip address is do:

   sudo ip addr

This will list all the network adapters on your system and show their addresses, if they've been given one.

As to firewalls:

Plugging the workstation directly into the Comcast cable modem puts your computer directly on the internet, where everyone can hack away at it trying to break in.  I always put some sort of router in between the cable modem and my computer.  They're available for cheap and are usually plug-and-play.  The router connects directly to cable modem, i.e., the internet, and gets a public address while the workstation connects to a private local intranet created by the router.  Nothing on the workstation can be accessed from the public internet unless I specifically change the router's configuration to forward ports through it to my workstation.  In the situation you described there would be no need to do such a thing.  When connected in this manner the computer can see everything on the internet, but nobody on the internet can reach the computer.

With that setup in place the firewall on your workstation really doesn't matter, but I always put one in place anyway.  If you decide not to go with a router between you and the public internet, then you definitely want to do the following:

1) Check to see if the firewalld daemon is up and running and is "enabled" to start automatically at boot:

   sudo systemctl status firewalld

2) If sytemctl says it can't find firewalld, then install it with dnf, start it, and enable it with systemctl:

    sudo dnf install firewalld
    sudo systemctl enable --now firewalld

Your system now has a firewall running with only the minimal ports needed open up on it.

Get to know the firewall-cmd command.  That's how you tell firewalld what to block/allow.  Like if you ever did want to open up for ssh, let's say.  Do "man firewall-cmd" and read all about it.  Here's a few basic commands to get you started:

To see your current firewall config:

    sudo firewall-cmd --list-all

Pay particular attention to the "interfaces", "services", and "ports" lines in the output.  "interfaces" lists the network interfaces that are part of this zone and use the rules defined within the zone.  firewalld has multiple zones predefined to support different use cases but that's advanced stuff you can explore later.  For now just make sure that the interface that your computer is using to connect to the network is shown here (Check the "sudo ip addr show" output to get the interface name if you forgot it.)  "services" is a list of names of ports that have been opened in the firewall.  There will be a couple of those. "ports" is a list of other port numbers, ones that didn't have predefined names, which have also been opened.  Initially that line will probably be blank.

To open up ports for services, learn these options:

    sudo firewall-cmd --add-service / --remove-service
    sudo irewall-cmd --add-port / --remove-port

Also pay attention to the --permanent option.  It determines whether the changes you make are only temporary or whether they are saved and restored after a reboot.

Hope this helps.

--
David King
dave at daveking dot com

--
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