I'm using an OpenVPN client on my RPI to tunnel traffic from clients in my LAN. Everything is stable, but the speed is terribly slow and I can't figure out what the bottleneck is.
I have a VDSL line with 50Mbit/s bandwidth and speedtest shows that I get about 5-6 m/s without the VPN:
wget --output-document=/dev/null http://speedtest.wdc01.softlayer.com/downloads/test500.zip
With the VPN I get only about 500-600kb/s, so roughly 1/10th of the speed. So I'm trying to figure out who the culprit is. Here's my setup and my test results for various potential bottlenecks:
CPU Speed With normal 700MHz speed settings the CPU is around 50-60% when streaming video, with overclocking it's even less. The CPU is NOT the culprit.
SD Card Speed I tested various cards, the fastest is a SanDisk 16GB Extreme with 45MB/s, giving me actual speed test results of 18-20MB/s. The SD Card is NOT the culprit.
OpenVPN Encryption Speed I'm using 256-bit AES CBC encryption, which I can't change due to requirements of my VPN service provider. Testing OpenVPN encryption speed gives me about 18MB/s for 256 AES. OpenVPN encryption is NOT the culprit.
Conclusion: I should get at least 15-18 Mbit/s with my setup, since all tests show that this is possible BUT I get far less and I would really love to get some insight about what else I could test for and how I could improve the setup to get a speed improvement.