[Russia] Investigate obsf4 blocking by protocol in mobile 4G in some ISPs
Since August 2024, we've seen a rise in user support tickets from Russia. Users reported issues with bridges provided by GetBridgesBot, noting that these bridges didn't connect/work for them.
Initially, we suspected that some bridges distributed via Telegram had been enumerated and blocked. However, more recent findings from @nina (full report: #40046 (comment 3125365)) suggest that obfs4 is blocked in mobile/4G network in some ISPs in Russia.
- The same obfs4 bridge connects successfully on residential connections, but fails on mobile networks (4G).
- Downgrading to 3G allows these bridges to connect to Tor without issues.
- WebTunnel bridges remain unaffected.
Just yesterday, a user reported that obfs4 bridges were not working on MTS/Moscow (AS8359). I checked the IPs of these bridges using MTS Looking Glass, and they were reachable, which could be an evidence of a new type of block (by protocol and not by IP).
Providers mentioned by users: Tele2, Beeline, and MTS.
edit: If you're reading this ticket and have access to MTS, Tele2, or Beeline, we would greatly appreciate it if you could share Tor logs with obfs4 bridges, a pcap, and any additional relevant information.
Please note that in this context, OONI Tor tests aren't particularly useful.
cc @meskio.