Solving the problem of connecting PPTP VPN via LTE from Yota

    To connect remote offices to the corporate network and telephony in the absence of wired providers, we use Yota's LTE and all-in-one DrayTek Vigor 2920VN routers.

    The other day, another set of DrayTek 2920 + Yota LU150 came to set up for me. This modem itself is a mini-router, and by default it gives the IP address connected to it via the USB host from the subnet, which in my case intersected with the local network. In the modem settings at the address % modemip% / network, you can change the range - and are available for selection.

    Changing the range to, I configured the router according to the standard, already tested scheme. And here is a bummer: the Internet is working, but the VPN tunnel to the central office does not rise. By the way, at this time everything works on the same router with the same modem in one of the remote offices. Devilry? No, engineers do not believe in the devils!

    At first, the suspicion fell on the VPN server (FreeBSD + poptop) in the central office. Having looked at the log, I noticed that DrayTek did not pass GRE packets. Stirlitz was wary. I plugged the modem into my laptop directly, created a VPN connection using regular Windows 7 tools - it also does not work, giving error 619. I checked it through my home provider - everything works. Just in case, I returned the address range on the modem to the previous - the same picture. So, the culprit is Yota.

    Time 2 am. I call support. The boy on the other end of the line clearly does not really understand what a VPN is, carries nonsense about routing and offers to connect an external IP as a solution to the problem. Okay, I am postponing the solution to the problem until the next day - should there be at least someone from the second line of support in the afternoon, even on the weekend?

    The day is coming. I call support. Switch to 2 line. I state the essence of the problem. I was immediately asked the question - “but have you, good citizen, changed the IP range on the modem”?

    The case turned out to be a bug in the firmware of the LU150 modem of the latest version 3.7 (namely, all modems with old firmware are automatically updated to this version): when changing the range, it stops passing GRE traffic, and changing it back does not help anymore. This problem is solved by manually changing the modem firmware to the test 3.7.4, which the tech support employee kindly sent me, saying goodbye: “the firmware seems to be solved in this firmware, but you still don’t change the IP range on the modem, but you never know.”
    Nowhere on the web was this firmware publicly available, so I post it here. (the link was removed at the request of Yota. Everyone who encountered the described problem can get the firmware via a call to support).

    At the moment, this problem is present in all modems from Yota, so you should not change the network settings of the modems before fixing the bug - they said in the support that this is not the only cant that breaks when changing the settings.

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