If you’re using the built-in unmodified hotspot on pretty much all phones these days, mobile data for the hotspot goes through a different apn. Your phone requests data on one channel, while hotspot data goes through another.
Comment on I have unlimited cellular data on my phone but not if I use it as a hotspot.
istanbullu@lemmy.ml 2 months ago
How can they tell if you are tethering?
bhamlin@lemmy.world 2 months ago
Michal@programming.dev 2 months ago
They must be sniffing traffic
orangeboats@lemmy.world 2 months ago
Not sure if it’s still the case today, but back then cellular ISPs could tell you are tethering by looking at the TTL (time to live) value of your packets.
Basically, a packet starts with a TTL of 64 usually. After one hop (i.e. from your phone to the ISP’s devices) the TTL is decremented, becoming 63.
What happens when the ISP receives a packet with a TTL value of 62 instead? It realizes that your packet must have gone through an additional hop, for example when it hopped from your laptop onto your phone, hence the data must be tethered.
orangeboats@lemmy.world 2 months ago
This also explains why VPN is a possible workaround to this issue.
Your VPN will encapsulate any packets that your phone will send out inside a new packet (its contents encrypted), and this new packet is the one actually being sent out to the internet. What TTL does this new packet have? You guessed it, 64. From the ISP’s perspective, this packet is no different than any other packets sent directly from your phone.
BUT, not all phones will pass tethered packets to the VPN client. Mine doesn’t! In this case, TTL-based tracking will still work. And some phones seem to have other methods to inform the ISP that the data is tethered, in which case the VPN workaround may possibly fail.
southernbrewer@lemmy.world 2 months ago
You can also just increase your laptop’s initial TTL by one and then they can’t tell.
Couldbealeotard@lemmy.world 2 months ago
How do you do this?
mhz@lemm.ee 2 months ago
That was a good read, thank you
mhz@lemm.ee 2 months ago
That was a good read, thanks