Port forwarding help!

Hello Everyone,

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i am trying to forward port 1723. Setup is:

AT&T Pace PLC Modem/Router

Netgear Nighthawk R7800

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I have forwarded the TCP/UDP ports on the nighthawk and set the Pace PLC modem/router to DMZ+ mode for the nighthawk R7800; However, when I check the port it is still closed. I have tried every solution I can think of. Please help!

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I would prefer to disable the firewall on the Pace PLC modem/router completely, but it seems that is not an option. I have also tried to forward the ports directly on the Pace modem, but it says the ip's are not in the same family.