Android connects to the phone network using a different type of connection (DUN) to send tethered data.<p>The code to do that is in android here:<p><a href="https://github.com/aosp-mirror/platform_frameworks_base/blob/355dbae680994002c48d7a66cb276a65393ecbbb/services/core/java/com/android/server/connectivity/Tethering.java#L1090" rel="nofollow">https://github.com/aosp-mirror/platform_frameworks_base/blob...</a><p>There is a setting you can set to disable it and make the provider treat all traffic as if it is non-tethered.<p><pre><code> adb shell settings put global tether_dun_required 0
</code></pre>
Considering how knowledgeable the HN crowd is on all things networking, it surprises me to see so much uncertainty on something so easy to check in the code!
Last year I called T-Mobile for some relatively minor reason and then got into a conversation about this "upgrade" I could get that would knock my bill down $20 a month, provide option X, Y and Z.<p>It sounded too good to be true so I just kept asking if I'd lose anything. I was assured, no, it's all benefit.<p>In the past if I had an internet outage at home I'd switch to to tethered phone and have no drop in speed. In fact, it was faster than work or home.<p>I recently moved and while waiting for internet installation suddenly found my tethered rate went down to .25/mpbs, whereas in the past it was up around 40mbps up and down. My phone itself reached these speeds via LTE. It became immediately apparent what I'd signed up for in my "upgrade" the year prior. I had been on some grandfathered plan that had no such restriction, and by "upgrading" sacrificed my ability to tether without moving to a One Plus plan.<p>Of course in the heat of all of this I asked myself that same question: "how does T-Mobile know?" Some of the suggestions here seem unlikely since I'm still able to get good speeds via the phone <i>simultaneously</i> while limited via computer. The MAC address thing seems compelling but I'm obviously not going to go around spoofing anything just because I got duped by my provider.<p>I've been a T-Mobile customer forever, but that kind of deception was really, really insulting.
>MAC address inspection<p>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.<p>>Inspecting the network packets for their TTL (time to live)<p>>TCP/IP Stack Fingerprinting<p>>Looking at the Destination IP/URL<p>Probably works, but I'd imagine it's pretty easy to bypass by proxying your connection through the phone.
Oh hell yeah, this is my topic. I really really really hate Comcast's poor reliability and cost in my area (seriously you can see me bitch on usenet today: <a href="https://groups.google.com/forum/#!topic/alt.online-service.comcast/nS0m4rEJDLo" rel="nofollow">https://groups.google.com/forum/#!topic/alt.online-service.c...</a> ) so I rely on a stack of various LTE providers that are comparable in speed.<p>I'm tethered right now to Sprint which really doesn't appear to give a shit. Their network is encapsulated to all hell since it's ipv6-only so I recommend decreasing MTU's when connecting to it (something like 1320 seems to work or sites like duckduckgo get blackholed). Sprint sucks unless you're line of sight to a band 41 tower and/or have a HPUA device.<p>T-Mobile detects tethering a matter of ways. I use a Moto E LTE 2015 (surnia) as a dedicated modem phone for them. I modified lineageOS 14.1 for my specific use case (namely just to add TTL as a target in the kernel for iptables). I also use Network Signal Guru to lock it to the meatiest band in my area (band 4 broadcasts at 20mhz)<p>The magical iptables option to pass is: iptables -t mangle -A POSTROUTING -j TTL --ttl-set 65<p>They detect certain services like playstation network, so you have to VPN that so it isn't counted. I disable ipv6 on the t-mobile APN too as an added layer of protection. Average use is around 250-300gb/mo, this is rural so it's unlikely it causes any quality of service issues (and I don't end up subject to deprioritization issues after 50GB)<p>EDIT: Should also mention at least T-Mobile used to do DPI on the User Agent sent by browser years ago. They don't appear to do that anymore (widespread HTTPS made that pretty useless). Back then I used to just get around port blocking by ramming my traffic through SSH dynamic port forwarding on port 143, normally used for IMAP. This was for T-Zones service level in the early 2000's.<p>Oh and for AT&T in the later 2000's I used to buy import phones that weren't in their system and use them on the non-smartphone unlimited plan until they got wise to that.<p>EDIT2: If you find ethics of this questionable, can't be hassled to figure this stuff out, and/or still want to use LTE unlimited where money is not a concern there's plans for that: <a href="https://unlimitedville.com/" rel="nofollow">https://unlimitedville.com/</a>
There is only one justified reason for phone companies to check if you are using your phone as a router, and that is when they provide unlimited data to your contract. Unlimited data is provided given that you are going to use it on your personal devices and not to act as an ISP to everyone around you. Other than that you generally pay for X GB of data and it is none of their business how you spend it.
Very interesting! I'm on a budget mobile service provider (Cricket), and only recently discovered that they disable using my phone as a hotspot on my plan.<p>I called them up, because I wouldn't mind paying a small amount extra every month to have that ability. However, they told me that they actually <i>couldn't</i> provide it with my <i>phone</i> even if I paid, because they didn't support my phone (Pixel). Then they tried to upsell me on "compatible phones"...<p>I used this phone as a hotspot with my previous provider, so I know it <i>can</i> be a hotspot. But I don't know much about the technical side of this. Does anyone know if what they're saying is plausible? (Ie, they can't offer it for my specific phone)<p>I briefly tried a few apps for this purpose, but none of them worked.
TTL is a nice cheap trick. I figure you can bypass it by adjusting your TTL to be +1 on the computer, or by running a VPN client that acts as a proxy on the phone.<p>This is another excellent question from the earlier days of stackexchange that are all now "offtopic". Its sad to see it consistently lose informative questions. Stackexchange's policy shift toward marking any slightly general question as offtopic is a sad state of affairs.
I am still annoyed (at Apple, to be clear) at the fact that my iPhone asks for carrier permission before functioning as a WWAN-to-WiFi NAT.<p>I have to carry two devices because of this. :(<p>Also in this list: Apple allowing video players to disable seeking in ads. It’s my hardware, fuckers.
Another note: just because you have a VPN running on your phone and have enabled Android's "always on VPN" and "block non-VPN traffic" options doesn't mean that devices connected to the phone hotspot will send their data over the VPN. You need to have it configured on the guest device as well.
>> This question exists because it has historical significance, but it is not considered a good, on-topic question for this site so please do not use it as evidence that you can ask similar questions here.<p>What reasoning would they have for that? It's an Android stackexchange after all.
Many years ago, on a UK network (I think it was o2, but might have been GiffGaff) I couldn't and didn't tether.<p>However, one app would make calls out with a User Agent that looked like IE6 which caused the network to disconnect my data and require me to phone up to get it unblocked.
I put Cyanogenmod on a device and tethered for years without any carrier warnings. Then I accidentally got a device with a locked bootloader and tethered by rooting it to switch a flag; I got a warning from that one. Then I got another open device, put LineageOS on it and tethered uneventfully for another couple years.<p>I'm sure my custom ROMs played some games to disguise the traffic, but at least on AT&T it seemed to work without a hitch.
I used to have the old AT&T unlimited plan. A few years ago, they cancelled it due to tethering. I called in to complain, as I know how to tether “illegally”, but hadn’t been doing it. Eventually realized that I’d connected my phone to my mother in-laws new Jeep Grand Cherokee, and the Jeep must have been making IP connections through my phone. Just to spite AT&T, I switched to Verizon.
I don't think it works anymore, but it used to be that you could get around tether-blocking in MetroPCS by simply setting your user-agent string to Chrome Android; they moved to something more clever because I guess enough dorks like me figured it out.
After several years of good service, I was accused by my telco (Cricket) of tethering without paying the special fee and my phone was disabled. Found this out in the middle of a trip.<p>The thing is, my plan did not require the extra fee when I signed up, and so that had been grandfathered in.<p>When the telco does this, you can switch to another one, but you cannot port your number. This would be like the postal service owning your street address. If they took a dislike to you, they could prevent you from using the address!
One thing others haven't mentioned is DNS. If your phone is trying to lookup Windows Update it's a surefire way of knowing this didn't originate in the phone.
One of my previous providers was literally looking at the browser user-agent header. If I just connected as normal via my phone, I was blocked very quickly. If I used developer tools in Chrome to pretend to be an iPhone or Android, it worked without complaint.<p>I'm not sure there is much else with which the network can tell is there?
I don't necessarily understand it, but for my Samsung note 8, I used a settings/flag editor and added 'DUN' to my LTE settings and was able to turn on Tethering, whereas normally, it would turn itself off after enabling "mobile hotspot".
My carrier started blocking requests from my tethered computer if they are made through a VPN ... that doesn't seem like it obviously fits into any category? Any guesses as to how they can do that?
The actual answer nobody is giving:<p>Q: How can phone companies detect tethering?<p>A: by working with Google and Apple to inject code in android and IOS to serve that purpose.