High CPU load while using PPTP
Hello.
My ISP gives me 830 mbit/s of download and upload, but speedtest sometimes shows the speed even more. There is only one connected device to my router and it's hypervisor with several virtual servers. An Ubuntu Server 18.04 is installed on hypervisor. One virtual server is using my ISP's IP address, so the Internet speed on it is about 800-900 mbit/s, for other ones I've rent cheap VDS servers just for IP addresses and installed pptpd on all of them. The ping between my hypervisor and these cheap VDS servers is 5-7ms. So Internet on my home VDSes works like this:
(Home VDS) -> (VDS in Datacenter via PPTP) -> (Internet)
The problem is, when I'm trying to run Speedtest on one of my servers with my ISP's IP address, the speed is about 800-900 mbit/s and router's cpu load is literally 0-1%.
But when I'm trying to run Speedtest on one of my servers with rent VDS' IP address, the speed is about 80-100 mbit/s and router's cpu load is about 35-45%.
Why is this consuming my router's CPU so much and is there a way to get rid of this?