Why am I unable to access my ViaSat modem with Safari using its IP address?

Q: Does your modem have router functionality?

A: Yes it does. Typing http://192.168.100.1 into Safari yields the following page. There is NO username/password challenge.

So, yes, it does have router functionality.

Q: Does it help if you use 192.168.1.1 instead?

A: No it does not. That address yields:

Suggestion: In the meantime, we recommend that you check if the issue persists when signed in on a different user account. 

Response: I don't understand how this could help. The Viasat device has no idea as to who I am other than the fact that I am connected directly via ethernet. The suggestion to use Safe Mode is equally puzzling to me. I have tried multiple devices (iMac, iPad, iPhone, MacBook Pro) all with the same result. I have also tried multiple web browsers (Safari, Firefox, Chrome) all with the same result. Finally, I have chatted at length with Viasat technical support and they are unable to offer any reasonable explanation as to why I cannot access their Gateway Modem to change the password and security settings. As you can see from the screenshot above, these functions are linked to but Safari et. al. are unable to access them.

This "feels" like a macOS security barrier intervening into an otherwise straightforward transaction via local IP address.

I was able to access the Viasat Gateway device and change the password using Safari under iOS which significantly lessens the urgency of this issue for me. Why macOS doesn't work is still an interesting question for me so I may pursue that at a later time.

Disappointingly, this access allowed me to learn that my WiFi network which is set to WPA cannot be configured to use WPA2/WPA3 Personal (AES) security type as Apple recommends but that is an issue I will have to take up with Viasat.

Thanks for all the helpful replies.