OpenVPN with OpenWRT very slow

[Bernd828]

Hello.

I opened a thread here, but nobody could help me.

OpenVPN connection stands for Perfect Privacy Service, but the download speed is very slow.

I hope that there are professional users here, that can help me.

Best regards

Bernd.

 

[Butterfly Bones]

Hello.

I opened a thread here, but nobody could help me.

OpenVPN connection stands for Perfect Privacy Service, but the download speed is very slow.

I hope that there are professional users here, that can help me.

Best regards

Bernd.

What router do you use? VPN is very intensive because of encryption requires fast processor(s) or two and having hardware encryption support really helps. Only the AC86U and AX88U have hardware AES encryption and multiprocessors.

https://www.snbforums.com/threads/openvpn-performance-of-the-rt-ac86u.41217/

 

[Bernd828]

What router do you use?

Asus RT-AC56U (2 Cores, 800 MHz). I configured OpenVPN client to Perfect Privacy service.

With AsusWRT, DD-WRT and TomatoUSB I did not have such download problems. I had 10-20 Mbit/s, but with OpenWRT I have download speed of <1.5 Mbit/s.

I tried this OpenVPN performance test:

openvpn --genkey --secret /tmp/secret
time openvpn --test-crypto --secret /tmp/secret --verb 0 --tun-mtu 20000 --cipher aes-256-cbc

Output was:

real    1m 17.68s
user    1m 17.40s
sys     0m 0.15s

3200 / 77,68 = 41,19 Mbit/s.


So theoretically at 40 Mbit/s is limit?

 

[eibgrad]

I have an ASUS RT-AC68U (800MHz, dual core). I normally get around 16-18Mbps w/ just about any OpenVPN provider, and regardless of firmware (dd-wrt, tomato, etc.). So very similar routers, and similar results. But I've never tried OpenWRT. And 1.5Mbp *does* sound like there is an issue. But what it could be is hard to tell, because the biggest culprit in poor VPN performance w/ most consumer-grade routers is NOT the lack of hardware encryption (although it does have an effect on the margins), but simply the fact that OpenVPN runs in user space rather than the kernel. And whether it's dd-wrt, tomato and its variants, or OpenWRT, they all suffer pretty much equally in terms of poor performance due to this fact. Why OpenWRT would be an outlier with numbers like that, again, is hard to say. Even if hardware encryption was somehow a factor, I can't imagine it having *that* much impact. Dropping from 20Mbps to 1.5Mbps is quite dramatic.

If I had to guess, I'd say you probably have some IP fragmentation taking place, due to an improper or mis-matched MTU size.

https://en.wikipedia.org/wiki/IP_fragmentation

But it's just a guess. OTOH, if the OpenVPN testing suggestions you should be getting far better performance, then I'm puzzled, unless the testing and actual OpenVPN client are using vastly different MTU settings.