Slow Internet Access via VPN

When recently configuring a VPN with a Mikrotik router, although access to the internal network was working successfully, any access to the internet via the VPN was very slow and unreliable.

Originally thinking this was to do with MTU/MSS, I spent a lot of time looking over the configuration to ensure that PMTUD was working correctly, and I couldn’t see anything wrong.

That was until I realised that if you fastpath traffic, then it skips all the VPN processing.

Don’t Fastpath VPN Traffic

So, in the end the fix was simple, I needed to add a couple of rules to the firewall filter that accepted traffic to and from the VPN before related and established traffic gets fast-pathed.

Once those rules were in place, internet access via the VPN worked perfectly.