Did the ISP give you a modem which you can connect to wirelessly or wired?
The Linksys WRT1900AC should already be connected to the model if the ethernet cable is connected to the internet port on the back of the linksys router. If you still want to login, then connect to the router (wirelessly) and locate its default gateway IP, open the default gateway IP in the web browser and you will be taken to the login page. Login, using the username and password ***** the router. As far as i know, WRT1900AC won't work with bridged DSL modems.
Because it is a WiFi only router not a DSL router. It can work with existing modems and routers if the modem or the other router has the internet but it cannot be connected to the internet directly.
The settings you are telling me about the PPPoE is not supported by this router. It may be possible that you just had this router connected to the modem and it picked up signals from the modem, which is generally how it works. To find out the IP Address, first connect to the router, wirelessly or wired, and then open a command prompt and type ipconfig /all it will display the default gateway ip address which is the one you need to open in a browser to access router's configuration.
That is how it should be. I just provided you the steps to get into the router above.
Welcome. If you need any further assistance - let me know.
Right now, are you connected to the modem or to the router?
What is the default gateway ip? you must not be connected to the modem if you are trying to get into the router.
Your internet is working then, why do you need to login to the router then? You can still login to router, but you'll have to connect to the router only (by disconnecting it from the modem) first. BUT since internet is already working, it doesn't make sense to login and change settings.
You need to disconnect the modem from the router. Then connect to the router (wirelessly or wired), then see what the default gateway ip is, and then access it in the browser.