I tried to log into my modem using address 192.168.0.1 per the manual, but it keeps telling me it cannot connect. I an trying to find some addresses for my wifi equipment.
Not sure why you want or need to do that. Your router should be set to auto-configure, using the data that is being pushed over from the modem. The router should also be providing DHCP address for devices connecting to your home LAN, including both wired and WiFi. Usually your home LAN will be 192.168.1.n, using the mask 255.255.255.0 and the server address will be 192.168.1.1 The modem GUI is often set up at 192.168.100.1
The TC8717T is a combo gateway unit. Are you attempting to adjust the router's network settings or see the modem's signal levels? Is the gateway set up in bridge mode?
I had this device for a couple of days years ago and had no access to the GUI menu as TWC or Spectrum had it locked out. Sometimes the address is changed so 192.168.100.1 may work.
Do you have access to the wifi settings on your My Account page?
HINT: You'll be able to get more help from readers of the forum if you mention WHICH advanced router settings you are trying to adjust (DHCP?) and tell us your LAN IP address plan. Also tell us what models of devices you are trying to interconnect.
There's only a few things that he could want to change in Advanced.
That is true - I had forgotten how limited this router is. The LAN subnet is always 192.168.0.n with server = 1, and there is no user adjustment to the DHCP range start or end values. It's a pain to assign static IP addresses on this unit since you can't adjust the DHCP window.
So back to my earlier question: "What are you trying to do?" If your network devices operate using DHCP the address assignment should be automatic and is based on their MAC IDs. About the only common device that requires the user to assign it a specific static IP address is an ultra-economy wireless-only printer that has neither USB nor ethernet built in, usually the two-letter brand. Those are a nightmare to set up unless you can edit the router's DHCP range.
Are you by chance trying to utilize a second router that is separate from the one already built into the TC8717T gateway? To do that you have to get Spectrum to switch the TC8717 into bridging mode, turn off DHCP, and turn off both of the internal WiFi band radios.