Slow speed on forwarded port

on my TP-Link TL-WDR4300 v1 with OpenWrt 21.02.0-rc4 I have forwarded port 1194 (TCP,UDP) from WAN to internal IP of Synology NAS where OpenVPN is running.

When connected from outside, VPN connection works, but it's extremely slow. Let's say, external upload speed is 70 Mbps, but real file transfer is about 7 Mbps. (tested from different external places, with different protocols)

Unfortunately I don't have an option to connect the NAS directly to internet to verify that the router is the bottleneck.

So, I'm asking you, experts, do you see any reason, why the router could be the reason?

Thank you

Port forwarding doesn’t affect bandwidth, so it is very unlikely that this is related to the router.

OpenVPN is a very demanding vpn in terms of the cpu power required to handle the encryption. If your nas doesn’t have hardware acceleration and/or a very powerful SoC, it is common to see very slow OpenVPN performance.

You might consider wireguard if you need better vpn bandwidth.

1 Like

Well, I changed the machine with OpenVPN server to i5 2core 4 threads 2Ghz and retested. Exactly the same result. With 70Mbps upload and 110Mbps download on opposite side, traffic at most 10Mbps.

Can you imagine any reason, why I can't achieve a higher speed?

I'm running out of ideas. I have no problem to buy a new router (which one.. ?) but I want to be sure, that this is the bottleneck.

Thank you for any idea :slight_smile:

Have you measured the speed, when connecting through VPN from a device inside the network?

Yes, connected with a phone at remote place directly, 70/70, connected to VPN 30/10. This 10Mbps upload is exactly the same what the user is complaining about. Real samba upload to my network less than 1MB/s.
The connection was to OpenVPN AccessServer running on i5 on port 443 (to minimize a risk of filtering by ISPs.. :frowning: )