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RT-AC1900P and openvpn experience

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ludo14

Occasional Visitor
Hello,

I setup an openvpn aes-128-cbc TUN TCP on the 1900p with a fios 100mbps connection.
The firmware is 3.0.0.4.380_3831
When downloading a single 900mb large file I get 2.35MBps / 18.8mbps.
What is weird to me is only one Core 1 is at 35% the Core 2 is 0% the memory is 54MB on status page.
Shouldn't it use both 1.4ghz cores?
I was expecting more speed since moving up from an rt-ac66u model.
What is a lower encryption setting I can use to increase the throughput?
Or what else can I do to increase the speed?

The server is a Synology ds916+ connected directly to router.
 
OpenVPN is single threaded, it cannot use more than one CPU core.
 
why ? as its not that big a jump in cpu or ram



sell it and get a better bigger router like the rt-ac3100 or rt-ac88u as the faster the cpu and the more ram the quicker the vpn is

I thought the rt-ac1900p had the same cpu as the ac3100 and ac88u?

I has the same cpu but half the ram.
 
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Setup OpenVPN on your computer as a test and see what speeds you get to determine if it is really that much restricted by your router.

Read in several places that a RT-AC68U gets ~ 50Mbit/s over OpenVPN (128bit encryption), so an RT-AC1900P should be able to get a lot better throughput then you get..

http://www.snbforums.com/threads/openvpn-estimate-performance-via-openvpn.33416/#post-268874

Edit: Interesting read about OpenVPN settings..
https://lowendtalk.com/discussion/40099/why-openvpn-is-so-slow-cool-story
 
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If it is single core it is not even using the whole core its only at 35% or ram so I don't get how a different router would improve things.
When I was using the 66u it would always go to 100% cpu.
I read all the links provided thank you and I will try other internet connection locations.
Are there lower encryption standards that are worth trying or is 128 low enough?
 
128 is normally lowest if you consider good enough security.

Btw, have you tried downloading from Synology cloud system(Cloud NAS)? And compare it to speed through VPN.

What is your home network speed 100Mbps download/20Mbps upload?

Also make sure that when you are testing, the network you connect to has fast enough Internet connection to test your VPN speed.
 

This should no longer be an issue with my firmware, as I initially added code to handle this about 18 months ago. After that, the OpenVPN devs have also improved the buffer handling by relying on the OS rather than an hardcoded value, so the workaround was removed.

Asus's stock firmware however still uses an older version of OpenVPN, and lacks the extra code I added at the time to handle buffers. Users might be able to implement the original workaround, in the custom config section:

Code:
rcvbuf 0
sndbuf 0
 
Asus's stock firmware however still uses an older version of OpenVPN, and lacks the extra code I added at the time to handle buffers. Users might be able to implement the original workaround, in the custom config section:

Code:
rcvbuf 0
sndbuf 0

Thanks for the clarification Merlin.

I read on some internet sources that people set the buffers to large numbers, like "rcvbuf 393216" / "sndbuf 393216". Would that be counter productive and/or only possible/beneficial when both server and client have the same settings applied?
 
Thanks for the clarification Merlin.

I read on some internet sources that people set the buffers to large numbers, like "rcvbuf 393216" / "sndbuf 393216". Would that be counter productive and/or only possible/beneficial when both server and client have the same settings applied?

Personally, I'm not a fan of overly large buffers. I don't know enough about OpenVPN's internal architecture to know if it would introduce latency into the data stream or not, but I wouldn't chance it, and just let the OS handle it automatically - the OS knows best. This is what newer versions of OpenVPN do.
 
I agree 100 percent with RMerlin's advice here - the linux 2.6 and later kernels do a very good job of managing those buffers.

The options in OpenVPN are there as the code base is intended to be "portable" in that it can be built and run on many different operating systems, and some may need those options to be explicitly set...
 
Personally, I'm not a fan of overly large buffers. I don't know enough about OpenVPN's internal architecture to know if it would introduce latency into the data stream or not, but I wouldn't chance it, and just let the OS handle it automatically - the OS knows best. This is what newer versions of OpenVPN do.
Thanks, was wondering about latency as well, will go with your suggested settings 'rcvbuf 0' and 'sndbuf 0'.
 

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