Really Inconsistent OpenVPN Speeds

Hi everyone,

I have a Linode 360 in the Atlanta Datacentre running Fedora Core 11, and I'm getting really inconsistent speeds using openvpn.

I mostly use it for streaming video, which was just fine for a long time, but then I started hitting periods where my bandwidth from my linode fell to well below 0.5 mbps. These periods were less frequent at first, but they now seem to be the rule rather than the exception and will last for 30-40 minutes before my connection will spontaneously return to its full speed. There doesn't seem to be any rhyme or reason for the slowdowns, and the problem isn't on my end as disconnecting from the VPN gives me full speed from my ISP.

Any thoughts on what might cause something like this? I've attached a pair of speedtests, one taken when things were working fine and another when a slowdown occurred. I've also attached a copy of the network graph from my linode dashboard; the tall points correspond to times when things were fine and the shorter points to slow periods.

Thanks for any insight you might be able to add.

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5 Replies

Given that your download speed is the only side affected (your upstream is the same in both cases), I'm going to lean on your ISP here. Since VPN traffic is occasionally used to hide BitTorrent from a nosy ISP, perhaps you've found an ISP that is QoSing your VPN traffic?

Try moving it away from its default port, perhaps.

That's a good thought… My ISP is usually pretty good about these things, but I'll try a different port and look into their throttling policy further. Thanks!

I'm having the same problem….did you ever manage to solve it?

I had a similar issue that was solved by switching ports, though I'm in China where the filtering and shaping is usually pretty rudimentary and easily avoided.

One suggestion offered to me at the time that's probably worth looking at though, have you tried switching TCP/UDP and port settings in combination and checked the effects of either/both on stability?

It's not uncommon for providers to shape based on these and it should be a pretty quick way to at least help clarify what's going on.

That makes good sense. I'm using a non-standard port 4672 for UDP. Seems to work ok.


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