Asus RT-BE86U - VPN server speed issues

[cassiopeian]

Hello,

I recently got the Asus RT-BE86U router.
Current firmware: ASUS-WRT Merlin 3006.102.3

I’m connected via a 100 Mbps symmetric 5 GHz connection (UBNT LiteBeam 5AC Gen2) on the roof of my house.
I have a public IPv4 NAT 1:1 adress.

The real speed on the WAN without VPN is around 85-100 Mbps. It's stable.

The VPN client (SurfsharkVPN) works fine when used on the router, phone, notebook, or PC. Speeds are nearly the same for both OpenVPN and WireGuard, limited only by the 100 Mbps connection.

The issue arises when I set up my own VPN server locally on the router, NAS or PC. The maximum possible speed for both download and upload is only around 35 Mbps. The speeds are similar for both WireGuard and OpenVPN servers.

I’ve also tried setting up WireGuard and OpenVPN on my NAS Synology 120j, Xpenology with a Celeron N4000 and my Windows workstation (Ryzen 5900X), but the speed remains limited to approximately 35 Mbps, despite all connections being on a 1 Gbps LAN.

What could be wrong?

I thought my hardware would easily achieve 100 Mbps. There is no traffic at all.

No QoS is applied. I’ve tried different MTU values, ports, changed encryption for OpenVPN but the speed is still low, with no changes.


ISP said:

Hello,

On our side, we provide connectivity according to the selected tariff, and we certainly do not filter your VPN in any way. Unfortunately, I have no experience with ASUS speeds, as we haven't used them long-term. If it supports another type of VPN connection, I recommend trying a different one. Most routers have varying speeds depending on the selected VPN client/type of encryption. If there is one with a higher level of encryption, speeds are usually significantly lower. On SOHO routers, L2TP or unencrypted PPTP tend to be the fastest, but PPTP is declining in usage due to security concerns.

There's no point in tweaking the MTU, as it will only lead to unsuitable fragmentation. The default MTU is 1500, but for VPN, it will naturally be lower depending on the type of VPN. If you don't have specific requirements from the other party, leave it at default.


Cloud somebody help me troubleshoot this behaviour?

Thanks a lot!

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[ColinTaylor]

The issue arises when I set up my own VPN server locally on the router, NAS or PC. The maximum possible speed for both download and upload is only around 35 Mbps.

Can you clarify this? Are you saying that if, for example, you run a VPN server on your NAS this somehow makes other devices on your LAN have slow internet speeds, even though none of their traffic is going through the NAS in any way?

 

[cassiopeian]

No, my internet and LAN transfer speeds are fine. Unfortunately, the VPN server speed on the router, NAS, or workstation is this low, even considering the very fast processor. I would expect the speed of the WireGuard server to be significantly higher than OpenVPN. And it definitely shouldn't be just 35 Mbps.

 

[ColinTaylor]

How are you testing this? Presumably you have a device on the internet somewhere that is connecting to your VPN server. That device is then running the speed test. Correct?

Bear in mind that in this scenario the speed test's traffic is going over your internet link twice. Test server <internet> VPN server <internet> client (and the opposite direction for upload tests). So end to end throughput could be significantly reduced.

 

[cassiopeian]

How are you testing this? Presumably you have a device on the internet somewhere that is connecting to your VPN server. That device is then running the speed test. Correct?

Bear in mind that in this scenario the speed test's traffic is going over the internet twice. Test server <internet> VPN server <internet> client (and the opposite direction for upload tests). So end to end throughput could be significantly reduced.

Exactly as you said. I connect to my home server on the Asus router, NAS, or workstation from another location, for example, using a 1Gbps connection.


However, the maximum speeds are around 30-35 Mbps, even though the server's location has a 100/100 Mbps symmetric connection. I initially thought the router's CPU was the limiting factor, but that's not the case. Even on a server running with an AMD Ryzen 5900X processor, the speed is just as low. And it doesn’t matter whether it’s an OpenVPN or WireGuard server.

 

[ColinTaylor]

From what you've said I don't think this has anything to do with your VPN server or what you're running it on. As I mentioned above I suspect this is a consequence of you saturating your WISP link with bidirectional traffic.

Can you try sending a large file to your NAS and calculating what throughput you get (e.g. converting MB/s to Mbps). Then try the same thing in the other direction.

 

[cassiopeian]

From what you've said I don't think this has anything to do with your VPN server or what you're running it on. As I mentioned above I suspect this is a consequence of you saturating your WISP link with bidirectional traffic.

Can you try sending a large file to your NAS and calculating what throughput you get (e.g. converting MB/s to Mbps). Then try the same thing in the other direction.

Thank you! I will check SMB transfer speeds over the VPN then.