Performance Issues with Dual VPN using Wireguard and Cisco AnyConnect Secure Client

Routers VPN, DNS, Leaks
1

My current setup:

Home VPN - Slate 2 Router running Wireguard server

Remote VPN Client - BerylAX running Wireguard client

Work Laptop - Windows 11 OS that uses AnyConnect Secure Client to connect to the corporate VPN

I directly plug in my work laptop into the LAN port on the BerylAX. The BerylAX is connected to my mobile phone via USB cable and internet access is using 5G connection with good reception. The BerylAX connects to my home VPN. On my laptop, I need to connect to the corporate VPN using Cisco AnyConnect Secure Client and all traffic is tunnelled once connected.

I am able to connect successfully, but some websites load really slowly and others do not. Performance speed is extremely slow.

I understand this is most likely related to MTU, but I have tried adjusting the MTU rate on the BerylAX to 1500, 1406 (default for Cisco AnyConnect), 1300, and none of these work.

Has anyone got a similar setup, or able to suggest a solution or tips to troubleshoot?

Thank you

3

Please try modifying the MTU of AnyConnect to the one equal to Wireguard MTU - 94 to see if it helps.

In your network topology, the MTU bottleneck is Wireguard (usually 1440/1420 maximum for IPv4/IPv6), so you need to modify AnyConnect's MTU to Wiregurd MTU - 94 to avoid fragmentation.

The 94 is the maximum possible header length for AnyConnect, as shown below.