Hello Manami
Router on a stick and firewall on a stick are both configured in the same manner. You must create subinterfaces that will each correspond to a specific VLAN. You do not configure this using “trunk mode” for the interface, as this is a configuration available only on Layer 2 ports of switches. In order to configure router (or firewall) on a stick, you simply use the same commands as those found within this lesson.
You can find configurations and examples of both routers and firewalls connecting to the Internet throughout the lessons on this site. You can take a look at the following section for everything that has to do with firewalls:
For more specific scenarios, please let me know what you would like to see, and I can direct you to the best lesson to look at…
I hope this has been helpful!
Laz