Slow throughput when using Windows OpenVPN clients vs Linux
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This one's not that easy to search on (or at least the terms I'm trying) as it unearths a LOT of posts with people running into how slow SMB can be over high latency connections / for small files, which I'm well aware of, and then a lot of older posts dating back to when an 8mbps broadband was high end. Then you get into buffer size / MTU tuning.
I've always known that file transfers can be a little slow over OpenVPN for remote users, but would often see 40+mbps which was just about good enough for those on general broadband. However, this is starting to become a bottleneck. So I've been looking into it.
I've got a Windows install run up as a VM for testing (to save the questions, yes, I get the same results on bare metal installs). I've tried the community OpenVPN client and OpenVPN connect
If I pull a single large file from an SMB share, I see about 40mbps, although it can start up at 100ish, it appears to fall over time. So far, I have no idea why it's so slow, nothing appears to be 'maxed out'
If I use exactly the same configuration file imported into Netmanager (Ubuntu), my laptop can pull the file down at 400mbps. If I hop to the Windows VM (which gets routed via my laptop), it gets the same speeds.
So it feels like I've found some very fundamental difference between the Windows implementation (OpenVPN + the TUN/TAP adapter) and running it directly on Linux.