Manage RT-AC88U router without an Internet connection

[AlHolden]

We have a RT-AC88U (and RT-AC68U on AIMesh) connected to the Frontier FIOS service. The AC88U is running 3.0.0.4.386_48263

Whenever I want to administer the router (using 192.168.0.1, or the router.asus.com address which replaces that IP), there's no response or a plain white page - unless the router has a working Internet connection.

Once the WAN is working, the router's admin pages all come up just fine.

This seems like a paradox, as I will never be able to administer the router (to fix a WAN configuration issue) when the router cannot contact the Internet.

Is there a setting I can change, which will allow me to admin the router from the LAN - when the WAN's not there?

[jzchen]

Please refresh my memory.  What is the router connected to, the ONT?

[AlHolden]

>What is the router connected to, the ONT?

Yes, the RT-AC88U Ethernet WAN port is connected to the FIOS ONT provided by Frontier.

Additional trivia;

• A Netgear wi-fi modem is connected to Ethernet port 1 as a WAN backup - that needs to be invoked manually because the automatic failover feature (by ping or DNS) hardly ever seems to work reliably.
• The RT-AC68U is connected to Ethernet port 8 for the AIMesh setup in the rental unit.

Thanks for your continued interest in my plight.

[jzchen]

I don't hear/read the term "WiFi modem" often.  From what I understand so far this is a 2nd WAN for the RT-AC88U, correct?  Where is it getting it's service from?  Is it in Bridge mode or providing an IP address to the secondary WAN?...

[AlHolden]

Oops I wrote that? Sorry, it's actually a CELL modem: https://www.amazon.com/gp/product/B08R813HLW

I got a cheap data plan SIM from a wholesaler and popped it in, then hooked it up to port 1 under the "Dual WAN" feature of the RT-AC88U. It's supposed to switchover to this whenever the main WAN goes down for a defined period.
Sometimes it does, but most of the time I need to flip it over manually. This is when the original issue comes up the most: I can't ever fix the router's WAN - because the router won't give me any admin pages unless it has a working WAN...

In my heart of hearts, I was hoping it was an odd confluence of settings I might have made. There's probably someone who works at Asus who would know what I could check, but I'll wager they don't work in support. 😉

[AlHolden]

I'm thinking that the ASUS RT-BE88U would be a compatible replacement.