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> but port 53 wasn't blocked, so a commercial VPN resulted in unlimited internet

The VPN would have to accept a connection over 53 though, right? This also seems like a great way to possibly bypass VPN blocking via DPI, which I've been hit with before on airlines when going over 443.

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Yeah, but it doesn't cost much to accept connections on all ports (AIM did it in the 90s).

DPI should be able to easily detect and block non-DNS traffic on port 53, as well as IP over DNS. Just a matter of configuration effort; but lots of networks lack configuration effort, so it's worth a try.

5190 continued well into the 2000s.

5190 was the default port, but if it wasn't open, any other port would work. You could have the client do a scan to try ports until one worked.

It'd be fascinating to get an at-scale timeline of ports blocked from common client connection points.

I assume it's drifted over time, but couldn't guess which ways / why. (Other than converging on blocking all non-443)

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