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Comment by gruez | Hacker News Reader

>MAC address inspection

AFAIK this wouldn't work because MAC addresses don't get forwarded to the next network segment. On android, the phone acts as a router (with its own DHCP server assigning devices a local IP address), so I doubt that information is getting passed on.

>Inspecting the network packets for their TTL (time to live)

>TCP/IP Stack Fingerprinting

>Looking at the Destination IP/URL

Probably works, but I'd imagine it's pretty easy to bypass by proxying your connection through the phone.

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> AFAIK this wouldn't work because MAC addresses don't get forwarded to the next network segment

Finally! I was scrolling down the comments, starting to think nobody on HN knew networking enough to notice this.

MAC addresses never "leave" the local network segment, so can't be used for tracking tethering unless the phone has code to forward this info on. But, at that point, the MAC address isn't really needed anymore ;)

Does 4G even use the concept of a MAC address? I'm not familiar enough with the protocol to comment, but MAC addresses are usually an Ethernet conecpt.

I believe it does use MAC addresses, just obviously the link layer is different. I'm not 100% certain though as I haven't gone deep into 4G!

It is difficult for an average user to set up a proxy, and there is still a possibility to detect PC by analyzing unencrypted DNS queries to MS domains for telemetry servers.

>It is difficult for an average user to set up a proxy

I'm sure that if there's enough demand for it, someone would make an app. A simple SOCKS5/stunnel server with a few buttons shouldn't be hard to make.

>and there is still a possibility to detect PC by analyzing unencrypted DNS queries to MS domains for telemetry servers.

This would really only be an issue if you don't have VPN killswitch set up on the tethered devices. Even if this can't be prevented, disconnecting phones because they made a connection to MSFT telemetry servers can be easily turned into a DoS vector. Want to mess with someone's internet? Put a bunch of img/script tags to MSFT telemetry servers on your site.

Back around the time this SE question was asked (2013), I was using an awesome open-source app [1] to tether on my iPhone. It was very easy to use, though you had to be able to compile and run it yourself, as there's no way it would be allowed in the App Store. I would be surprised if something similar didn't exist for Android.

I needed to tether on train rides a few times a year, which was really not worth paying for the service. Nowadays I can do it without an exorbitant extra charge (aside from the extra data that tethering guzzles), so there's no need for it.

[1] https://github.com/tcurdt/iProxy

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