OpenWrt OpenVPN NordVPN Slow Connection

I followed a guide to setup My OpenWRT Firmwared Router with the OpenVPN software to connect on one of NordVPN's servers.

It successfully connects onto any NordVPN servers, but when using a Speed Testing tool: the download speed is reduced by half...

I did 3x different tests

  • with openvpn enable on router
  • with openvpn disabled on router (connecting directly on internet)
  • with NordVPN software on my Windows PC using same server configured with openwrt's openvpn

The results with the NordVPN software on Windows PC matches my provider speeds - being the same results from having openvpn disabled in openwrt on router (which is great)...

But the results from connecting on that same server by using openvpn on openwrt has a download speed that's reduced by half (if not more)...

...Would anyone be able to point me in the right direction on how to improve that?...

Router Specs:

  • Hardware: TP-Link AC1750 Archer C7 V2
  • Firmware: OpenWRT v19.07.7

Note:

  • I checked the CPU / Memory load of OpenWRT's OpenVPN and it's under 5%...
  • And I also set up openvpn by following this following guide (while using my own preferred labelled names):
    [guide] OpenVPN client using LuCI - nordvpn

short answer: Your router is too slow for vpn stuff. You should remember what building a vpn tunnel means, it means a lot of crypto/math operations and the cpu in your router is a little bit slower than the one in your pc.

Why do you think you get the same speed when using no vpn?

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I was thinking that the CPU could be the answer but I was assuming that by having a low CPU load that maybe the answer could've been something else...

While talking about CPU, another question...

  • Would you say that TP-Link AC1750 Archer C7 V2 has a more powerful CPU than the Linksys EA4500?
  • Or would you say that the Linksys one have a more powerful CPU to handle OpenVPN a lot better than the TP-Link one?

...if ever there's any of a significant difference in CPU power... ??

cipher AES-256-CBC
What speed have you achieved with Archer C7? I suppose, about 8 Mbit, it is good speed for this SoC.

IMHO you should choose SoC with hardware support of AES-256.

I have not used Linksys with Marvell, but I suppose, it would be much better.

Yes, give or take it was around 7-8Mbit

OpenWRT/VPN (server=ca1470)
-Down = 7.24 MB/s
-UPLD = 4.51 MB/s
OpenWRT/VPN (Disconnected/Reg ISP)
-Down = 12.1 MB/s
-UPLD = 5.11 MB/s
NordVPN Software (server=ca1470)
-Down = 12.1 MB/s
-UPLD = 5.11 MB/s

Nordvpn offers wireguard, maybe you can use this as you will get around 50Mbit

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fwiw, the C7 v2 is powered by 750MHz QCA9558. It is old than 720 MHz QCA9563 found in later C7 models.
https://openwrt.org/docs/guide-user/services/vpn/openvpn/performance

The later QCA9563 maxes out at 17 mbps via ethernet (even slower via wifi) with openvpn protocol.

In the case of OpenVPN the only possible solution is to switch to 128-bit encryption.
All other tweaks that could boost your OpenVPN performance will give no effect because of insufficient CPU power.
If you are not comfortable with 128-bit AES you should move to Wireguard.