GL.iNet GL-AXT1800 for travel. Robust VPN config?

100% in IT is not really possible. Mostly never. They are pretty leak free, but it depends on different things. Using a repeater in a hotel is one of those things that might leak a few packages, mostly DNS.

Just don't use your companies' laptop to enable the repeater mode and login into the captive portal. If you turn your laptop on after the router is connected to the hotel's Wi-Fi, all will be fine.

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