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Yesterday I got a VPS as a dedicated machine for OpenVPN, I set it up and ran a speed test today, what I saw astonished me:

With VPN:

enter image description here

Without VPN:

enter image description here

The VPN is situated in another country, on a different provider.

As expected the latency is slightly higher on the VPN, but I never expected the download speed via the VPN to be just below double that of my normal standard non-VPN connection. The upload speed is to be expected since I would've thought it'd be easier for my ISP to throttle that than downloads. I've always thought that a VPN connection will always have a lower speed than that of the normal connection, but clearly I'm incorrect.

I first thought that the result is anomalous, but I re-tested it a couple of times (for different speedtest servers) and had similar results, therefore the liklihood of three anomalous results in a row is nil. I also restarted both the VPS and OpenVPN server with service openvpn restart (the VPS' OS is Ubuntu 14.04 64 bit), same result.

How is this possible?

This is the connection speed of the VPS (455Mbit/s,256.91Mbit/s):

enter image description here

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    Perhaps OpenVPN somehow performs compression on the data ? Or maybe Net (non)Neutrality is to blame.
    – Jonas Czech
    Commented May 26, 2015 at 9:37
  • @JonasCz It's true that I enabled compression on the OpenVPN server, but I didn't think it would have this effect on the speed. Might test by temporarily disabling the compression. Then again, even if it was compressing the data surely it shouldn't be higher than the 24MBPS I pay my ISP for?
    – AStopher
    Commented May 26, 2015 at 9:37
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    Compression might well give you more speed than you paid for, as you would then be able to transfer more data in the same amount of time, thus giving you higher speed. You are still only transferring 15 Megabits per second through the cables, but your compression is letting you put 30mbps into that. And yes, compression could reduce the size of your data by half.
    – Jonas Czech
    Commented May 26, 2015 at 9:51
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    Interesting that compression can have that big an effect. Going to bookmark this as reference for anyone who asks if it's worth the CPU load.
    – Arthur Kay
    Commented May 26, 2015 at 18:21
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    @cybermonkey you are awesome :D, now just to use ubuntu and not CentOS...
    – td512
    Commented May 27, 2015 at 7:53

2 Answers 2

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This was to do with the OpenVPN server's compression feature, meaning that more data can be sent at once.

This, therefore, meant the connection was faster. To confirm this, I disabled the compression feature and had this speed:

enter image description here

...whereas with compression enabled, consequently had this speed:

enter image description here

It seems that had I used a standard VPN other than OpenVPN I wouldn't have seen this significant speed burst.

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    This happens because the test data probably has very low entropy (like all zeroes or whatever) and can thus be compressed a lot.
    – Daniel B
    Commented Mar 2, 2017 at 6:32
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I use 64/4,5 Mbps pure internet connection. But when I connect to corporate server through AT&T VPN then I have 2Mbps (yes, download, it is, as they say, standard corporate policy) / 20Mbps (UPLOAD 4 times faster than I'm paying for to my cable provider!!!).

I don't belive in VPN compression positive impact (as opposite to extra VPN load's negative impact :)), as speed test uses 10 GB zipped file for testing and I don't think this file can be compressed more, even if the individual UDP packets load is recompressed (as I know, VPN uses UDP flow ensuring TCP like level by itself).

The only reasonable explanation I met was, that due to fact AT&T owns the most skeleton in the Europe, the providers are obliged to route AT&T traffic without any limitation. Must be aware that cable modem I use is capable for achiving 440/120 Mbps speed via 8/4 down/up channels. And probably the QoS is done only at provider's L3 infrastructure.

Tomek

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