Could it be that IPSec VPN ports in blocked by China or Alibaba Cloud?

[Andrea1701]

We started to implement IPsec on cloud ECS instances and after couple days of working it stopped to work. Debugged it and seemed that packets with source and destination UDP 500 port are filtered. After that tried to change my source IP in Local Datacenter side - and it started to work. Don't know how long it will. Could it be due to whole China policy to block VPNs in 2018 ? Thanks

[RedSon]

Perhaps. If you suspect that your traffic is being blocked, try using a port that you know will be open like port 80.