Very slow speed over IPSec (Fritz!Box)

[TheEastWind]

Hi everyone,

I'm getting very slow speeds over a VPN set up between two routers (2x Fritz!Box 7390). The routers set up a VPN between them so I get the subnets 192.168.0.x and 192.168.1.x. I have set up appropriate NAT holes, even though for the VPN that shouldn't matter

I'm getting speeds in the 2 kb/s range, sometimes changes aren't even propagated to other clients.

As far as I can tell from the official documentation, the VPN uses IPSec/IKE with AES encryption. I have no real influence on any parameters of the VPN connection. All other applications work fine over VPN.

I've seen two similar threads (one with the exact same routers), but no replies.

Thanks and regards,

TheEastWind

[GreatMarko]

Are your devices able to establish direct connections to each other through the VPN (indicated in BitTorrent Sync by a two-way arrow icon), or only indirect connections? (indicated by a "cloud" icon) ...as this will greatly affect speed!

[kos13]

Could you please follow steps here and refer to this thread in your email?

[rdebath]

Chances are the peers will not use the VPN unless you set them up as known peers.

But I'll only say that because I'm allowed to guess, kos13 has given you the real answer.

[dmitry]

Try to increase MTU value to 1500

[kos13]

Please let us know if the problem is resolved with MTU = 1500.

[TheEastWind]

Sorry for the delay. My MTU is 1500 anyway. Both connections are extremely stable VDSL2 connections with not troubles outside of this whatsoever.

I have disabled the VPN connection, disabled both Windows firewalls, to no avail. I double-checked the NAT port forwarding, tried out µTorrent on both computers, using the same ports, which works fine.

Interestingly, after some messing around, I found out that the sync works one way - but not the other. That is, files from one network (machine called boreas) are being synched to the other (machine called atlas), but not the other way around. Both clients propagate changes, initiate transfers, but the transfers only work one way; the other way around, the transfer just sits there in the Transfers tab with 0.0kb/s speeds.

Third test: Got my sister to install on her computer (yet another network). Sync works fine between hers and mine, she can sync fine with the network containing atlas, but I get nothing from atlas.

In summary:

Three networks (atlas, boreas, other). Atlas & Boreas configured with NAT forwarding and disabled firewalls, other network as-is. Boreas->Atlas, Boreas->Other, Other->Boreas and Other->Atlas work fine. Atlas->Boreas doesn't.

I have sent all this (and the log files) in an email to syncapp@bittorrent.com

[kos13]

Thank you for logs, we will analyze them and will get back to you.

[Peter_NL]

Same routes same problemen. fritz!box issue

[TheEastWind]

Fixed it: slightly embarrassed about this, but settings "lan_use_tcp" to true fixed it. I have to admit I never even thought this might be the issues as I couldn't see any reason for TCP to pass through the NAT/firewall, but not UDP.