Yes, this is the serious problem
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I have 100-megabit fiber (unfortunately, higher fiber is currently not available in my area).
As a second ISP I used an old modem with a sim.
And I made sure to hook up with “a third ISP” as well, taking advantage of my cell phone’s HotSpot “in combination with a WiFi repeater.”
IPFire 3 has “everything included.” So I was told in another post. And that solves the problems of double nat
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