@MR.S will look into that, thank you !

@MR.S well, thanks for your help. I'll look into the V2 version then.

@MR.S thanks for your reply. You were right, I was looking at the V2 datasheet, my bad. Yet, when looking at the V1 datasheet here : https://www.tp-link.com/fr/support/download/tl-er7206/v1/ is says...

Both on the router's site and on the client's site there is a 900Mbps fiber internet connexion. The VPN (L2TP over IPSEC) however never goes faster than 110Mbps. I have been working on that for days...