@dafyre My small addition in french : https://www.canaletto.fr/post/zerotier-site-to-site

@dafyre And dont use Debian Buster (10), prefear Jessie (8) or Stretch (9) max at this day

@dafyre I think I found the problem, my VM Debian 9 which serves as router had only 1 GB of RAM and 1 vCPU, I made x 2 and it is much better !

Here we see the difference before and after ...

@dafyre Problem with this config : we lose 90% (or more) of the flow. It's not nothing !

Iperf from a ZT client in Azure to a ZT router on my datacenter (1 GB)
[ 4] 0.00-10.00 sec 112 MBytes 94.4 Mbits/sec sender
[ 4] 0.00-10.00 sec 112 MBytes 94.4 Mbits/sec receiver

Iperf from a ZT client in Azure to a lan machine via the same ZT router my datacenter (1 GB)
[ 4] 0.00-10.00 sec 112 MBytes 9.5 Mbits/sec sender
[ 4] 0.00-10.00 sec 112 MBytes 9.4 Mbits/sec receiver

My ZT routers are Debian on ESX VM

Or can be the problem?