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For some reason, I was downloading something at 300kb/s. Then I turned my VPN on and the download speed jumped up to 1.3mb/s.

Why is this? Is it because the VPN server reduces the jumps between me and the server?

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    @Divin3 - It is entirely possible for a VPN to speed things up and reducing latency. I've covered the speedup in my answer. In addition to that, a VPN can reduce latency (a bit, by compression) or a lot (via an alternate path - particularly where load balancing is being done to remote locations where cables are constrained and supplemented with Satellite capacity - less common now though). I also note that latency on a small link can vary significantly with usage. If VPN endpoint is on a router in the path, latency does not always go through an exfra gate - common on corporate VPNs – davidgo Apr 28 '16 at 22:28
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    @davidgo - by latency I mean the response time. For example if you play an online game the latency can't really be lower if you use any sort of VPN. The download/upload speed (bandwidth) is a different question. – Divin3 Apr 28 '16 at 22:45
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    @Divin3, the latency could certainly be lower depending on how the ISP treats certain types of traffic. Also as davidgo pointed out, it's entirely possible the VPN takes a different/better path. It's not impossible by any means... I've utilised VPNs to reduce latency before, it's uncommon but not unheard of. – user161778 Apr 28 '16 at 22:56
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    @Divin3 - I understand latency, and was commenting on that. A typical satellite connection is about 600ms, the same over cable could be less then 120ms. Also google Buffer Bloat - something that alternative paths can also route around sometimes to reduce latency. – davidgo Apr 28 '16 at 23:36
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There are a few possibilities - unfortunately, the number of hops is irrelevant.

The first is compression - if the data you were downloading is uncompressed, and your VPN offers compression then this could explain it - however most files transferred are likely to be compressed, so this is not as likely as it would seem at first blush.

The second and third options are related, and have to do with your ISP's connectivity and restrictions. Your VPN has found a faster path to the destination data then directly - which could be because -

  1. The ISP has multiple connections, and the direct connection to the data is constrained. The VPN goes across a different connection, which in turn has better connectivity to the source of the data you are pulling, thus you are routing round the congestion.

  2. The ISP is shaping certain kinds of traffic - possibly by type or destination or both - it could even be by content/payload - but that is less likely. By using a VPN, your traffic is being given priority or not being capped, so you are getting better speed.

There are some other possibilities, but these are again less likely - it could be that the VPN is using UDP while your download would typically use TCP, and different optimisations (MTU for example) are allowing better use of your connection. Again, this is possible, but unlikely - chiefly because you would expect either a much smaller or much greater difference in speed.

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  • You beat me to the punch :-) - but I actually like your answer better. – LSerni Apr 28 '16 at 22:14
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    Does it really make sense for an ISP to give VPN traffic a free pass given it's a tunnelling protocol? I would expect everything to be rate-limited by default and only some services to be prioritized by whitelist. – Thomas Apr 29 '16 at 2:37
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    @Thomas A lot of ISPs use transparent proxies for certain things like HTTP. The idea is that they can cache results to speed up page fetches and reduce bandwidth requirements... which of course does nothing positive for dynamically generated content. What ends up happening is they introduce additional pointless delays for most modern content. There's no point trying to proxy or cache VPN traffic so it doesn't get the additional delays. – Corey Apr 29 '16 at 5:11
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    @Thomas the problem is that VPN traffic is not easily identifiable - it can be disguised to look like other kinds of traffic (including VOIP - which requires low latency), and also corporates use VPN's a lot, so they may get a better class of service. Also, Most VPNs use UDP rather then TCP which is used by most download protocols. Its A LOT easier to reduce performance of a TCP connection then a UDP connection without causing issues as TCP takes a hint to slow down when packets are dropped (by design), while UDP doesn't. – davidgo Apr 29 '16 at 5:32
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    It's also possible that the server on the other end is throttling based on your ISP: usatoday.com/story/tech/news/2016/03/25/… is a recent example of this (people were blaming Verizon/AT&T for slow Netflix, but it was actually Netflix throttling on purpose). I don't see in that article, though, whether it was based on IP (which would affect people connected to a hotspot, but not the device on a VPN), or something on device detecting the carrier. – childofsoong Apr 29 '16 at 17:50

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