Throttled at 500 KB/s - AirVPN Wireguard via Gluetun+qBittorrent on Synology NAS

[LeeO 0]

Major performance issue (Hard Cap at sub-1MB/s)
Hardware: Synology NAS [DS918+]
OS: DSM 7.x
Container: Gluetun (image: qmcgaw/gluetun)

 

Hi everyone,

I am experiencing extremely slow speeds with AirVPN (Wireguard) configured via Gluetun on my Synology NAS. Despite having a high-speed fiber connection, my downloads inside the container are currently capped at approximately 500 KB/s.
 

Interestingly, when I first tested Wireguard with a MTU of 1280, the speed briefly hit 30 MB/s, but it has since dropped and won't go back up. Furthermore, when switching the provider to Private Internet Access (PIA) using OpenVPN, I easily reach 15 MB/s, which suggests the NAS hardware is capable of more.
 

Here is my current Docker Compose environment configuration for AirVPN:
 

environment:

• VPN_SERVICE_PROVIDER=airvpn

• VPN_TYPE=wireguard

• FIREWALL_VPN_INPUT_PORTS=3xxxx

• WIREGUARD_PRIVATE_KEY=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

• WIREGUARD_PRESHARED_KEY=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

• WIREGUARD_ADDRESSES=10.xx.xx.xx/32

• WIREGUARD_MTU=1280

• SERVER_COUNTRIES=Belgium

• VPN_IPV6=off
   

Technical observations:

• Speed Test: Tested via "sudo docker exec -it gluetun-wireguard wget -O /dev/null https://proof.ovh.net/files/100Mb.dat". Result is consistently stuck at ~500KB/s now.

• MTU: I have tried 1420, 1320, and 1280. Only 1280 showed a brief spike to 30 MB/s before crashing down to current speeds.

• CPU Usage: NAS CPU remains very low during tests (< 15%).

• Connectivity: The tunnel establishes perfectly and I am assigned the correct AirVPN IP.

• Comparison: PIA (OpenVPN) reaches 15 MB/s on the same machine/network.

• ISP/Hardware: Outside of the VPN container, the NAS reaches full fiber speeds (900+ Mbps).

It feels like there is an invisible hard cap or a massive packet fragmentation/dropping issue specific to the AirVPN/Wireguard setup on this device.
 

My questions:

1. Why would the speed peak at 30 MB/s once and then stay throttled at 500 KB/s?

2. Is my syntax for WIREGUARD_ADDRESSES and FIREWALL_VPN_INPUT_PORTS correct for the Gluetun/AirVPN implementation?

3. Are there any known Docker-on-DSM limitations that specifically throttle Wireguard UDP traffic over time?
   
    

Any insights or troubleshooting tips would be greatly appreciated.

Thx !

[Hypertext1071 11]

Is it possible you accidentally set a speed limit in qBittorrent? Also if you want to optimize speeds, I think you could try specifying servers (instead of just country) and testing them one by one.

[LeeO 0]

Hello,
no limit was accidentally set.
I've already run server-by-server tests; the Belgian servers work best, and despite speed tests on those servers showing 30 MB/s, the speed via qBittorrent doesn't increase.