Awesome!
Yes. This is quite common. For cable modem service in the US, this usually is just one MAC (all others will be ignored). But typically on a cable modem, you can reboot the cable modem to clear the 'learned MAC' -- but the way other ISPs work may be different.
The ISP may allow several MACs, but only a certain number before additional ones are just denied service. Or, it is always possible the ISP had some sort of block on the specific MAC on the device that wouldn't work (could be for any number of reasons, just a theory that I cannot backup with anything specific).
Sure.
Yes, that's fine.
If things are working as expected...
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Thanks! 