In the series, ‘spare me the lecture, just tell me how it works’, here is a bunch of quick reminders about your ip configuration on your Ubuntu linux box.
ifoncig.me is a handy website that will show you all kinds of information in your web browser, such as your public facing ip, hostname and other goodies about your connection. take a look
From the command line this can be used too, and will response without the clutter you may see in a browser. To do this, just use:
which will respond with the ip you are using for your internet connection.
Next, to show your local configuration, use
If your system uses netplan, and you want to set a static ip address, move into the directory /etc/netplan, which should contain teh file to configure your ethernet card. The file may be named different, but that doesn matter.
:/etc/netplan# ls 50-cloud-init.yaml
Edit the file to switch between options. Configuration for dhcp:
network: ethernets: eth0: addresses:  dhcp4: true version: 2
Configuration for using a static ip address
network: ethernets: eth0: addresses: - 10.25.9.11/22 dhcp4: false gateway4: 10.25.9.25 nameservers: addresses: - 10.25.9.12 - 10.25.9.13 version: 2
See also: https://netplan.io/examples