Accessing a cable modem from inside firewall?

[jerrac]

I want to access the web ui for my cable modem. It's documentation says the default ip is 192.168.100.1. Of course, since the modem is outside the firewall, that address just plain won't work for it.

I've googled around, as well as searched this form. So far the closest I've found to anything helpful is this: https://doc.pfsense.org/index.php/Accessing_modem_from_inside_firewall

Unfortunately, that's for pfsense. The UI for OPNSense is not the same... And there's not enough background there, or in my own head, for me to figure out where in OPNSense I should make the changes.

So, can someone tell me how to access my modem's UI? Maybe translate the pfsense wiki page into something for OPNSense, or if that's not actually how I should do it, point me in the right direction?

Thanks!