NordVPN-IKEv2 slow NET speed

[msatter]

I’d really love to understand how an MTU issue can cause much lower speed but otherwise working connections. Okay, each packet occupying the whole MTU gets broken into two thanks to IPsec processing which adds extra bytes to it, but that should cause half the speed at worst. And if they didn’t get through at all due to wrong MTU, the TCP sessions should completely fail, not just become slow.

I have not solved it but could narrow it down thank to support by Mikrotik.

IKEv2 and MTU (MSS / PMTUD)

Support came back to me on this and despite it was not solution it helped me in optimizing my MSS/PMTUD line in Mangle even more. Till today I looked if a connection was marked as an IKEv2 connection by me and then apply the static/fixed MSS of 1382 in my case. I could not differentiate between down and upload and only upload needed the change in packet size. In the support mail I received was written that the packets, I sent in the trace, were 1460 bytes and when trying I put just that number…