OPNsense IN FRONT of router

[MoCA_Mocha]

Right now I'm just wanting to setup OPNsesne between my computer and the router that gives my computer an Internet connection. My router is an Asus AC68u flashed with Asus Merlin and I have added the OPNsense MAC address from its LAN port to use a unique IP address outside of DHCP for the  LAN port of the router. So in essence a static IP I guess you can call this for OPNsense's LAN port.

Setup goes fine at first but after a while I can't access the browser config for OPNsense at 192.168.1.1 on the OPNsense LAN port and I never do get Internet access even after creating some basic pass through WAN/LAN rules in OPNsense. The OPNsense WAN port is where I have the router plugged into from the router's LAN. AM I looking at setting this up in some kind of bridge mode due to the way I want to set this up right now with the router BEFORE the firewall? I saw this tutorial. Are these all the steps I need to follow or something else?

A quick topology of what I have here.

                                         WAN - LAN --> WAN - LAN -->                   
INTERNET ---> MODEM ---> ROUTER ---> OPNsense ---> MY COMPUTER.

Modem is of course in bridge mode and always has, but this isn't my concern here. It's the router to firewall I'm having an issue with.

[cookiemonster]

It is perfectly possible but there are different possible use scenarios of a router after router setup and they are a bit of advanced setup, hence "not working" right now.
If all you want to do is put opn inline like that to play, I'd say it is too much faff for it.
If you want to actually have two routers like that permanently, then have a look at this https://homenetworkguy.com/how-to/use-opnsense-router-behind-another-router/

[phoenix]

Why do you have a modem and a router in front of OPNsense or is the modem/router one piece of kit?

[cookiemonster]

he's got his modem/router from the isp phoenix, but he wants to use his own router however the isp requires him to use their provided modem. So he has to leave it in place and put it in bridge mode so he can delegate routing to another device of his choice.

[phoenix]

That's what I thought but the diagram indicated they were different 'boxes', in any case if the modem/router is in bridge mode surely there wouldn't be any firewall active?

If the modem/router is in bridge mode I'd suggest you just set up and 'normal' installation of OPNsense rather than a Transparent Filtering Bridge.

[cookiemonster]

Of course, agreed. I assumed perhaps wrongly the OP wanted to put his opn in between as in the first post as a test thing or semi-permanent thing.

[MoCA_Mocha]

Bump

[Demusman]

What are you bumping?
This is a basic setup with no changes needed to work.
You need to be more specific here.
It's being assumed that your modem is a combo modem/router but you never said that and the asus model is just a router.
Your title is backwards, Opnsense is being put BEHIND another router.

What are you trying to achieve here?
Do you want the public IP on opnsense? If not just plug the modem to wan of asus, lan of asus to wan on opnsense, lan of opnsense to pc. Done.

If you do, get rid of the asus and plug opnsense into the modem. Done.

Explain what you really are trying to do with 2 routers.