Blocking Modem GUI (AT&T)

Hello everyone,

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I was wondering if anyone had success blocking the gui for att modems. For example, my modem is 192.168.0.1 and the only client is a router which is 192.168.1.1. I want any devices behind the router to be prohibited from accessing the modem. AT&T modem GUI shows WiFi password in plaintext along with device info so this has to be fixed ASAP. I have dd-wrt on the router and another router with tp-link managed switch software that I could use.

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Thanks!!