avery

Wetware Developer

Problem

My phone’s rom, grapheneOS, permits tethering, but my carrier bans it1. So, my carrier blocks anything I tether.

There are 4 vectors I’ve read about for tether detection2:

  1. Packet TTL
  2. Phone defaults are configured to expose tether status to carriers.
  3. TCP/IP stack fingerprinting. Default implementations vary by OS
  4. Deep packet inspection. Mobile devices don’t connect to e.g. a windows update server

Solution

  1. Incrementing the default packet TTL on my desktop/laptop spoofs my phone’s TTL.
  2. Variables stored in /system/build.prop. Specifically, tether_dun_required needs to be 0, and net.tethering.noprovisioning needs to equal true. You need root access now or during the OS build step to edit /system. I don’t think this can be addressed on iOS.
  3. Too inconsistent to be the sole reason to block packets; I ignored this
  4. A VPN fixes this easily

So now I’m pushing this post on my desktop from my phone’s hotspot3. I don’t know how many of these fixes are actually necessary; that probably varies by carrier. I succeeded after setting up a VPN4, incrementing TTL, editing build.prop vars, and rebooting my desktop.

  1. unless I pay extra. America doesn’t even have net neutrality ↩︎

  2. from stackoverflow and xda-developers ↩︎

  3. Comcast doesn’t provide 100% uptime, so the redundancy is nice. ↩︎

  4. $15/mo cheaper than the hotspot premium ↩︎