Please check the Nat VPS activation email sent, where the Server IP is the public IP and the Main IP is the intranet IP.
Take the public IP as 93.184.216.34 and the intranet IP as 10.1.1.102 for example:
The SSH port is 93.184.216.34:61102 -> 10.1.1.102:22.
The Third segment of the intranet IP is "1" and the Fourth segment of the intranet IP is "102", so "6" + "third segment" + "fourth segment" = "6" + "1" + "102" = 61102.
The mapping of the other 10 ports is 93.184.216.34:11020-11029 -> 10.1.1.102:11020-11029. The Third segment of the intranet IP is "1" and the Fourth segment of the intranet IP is "102", so "1" + "102" + "(0-9)" = "11020-11029"
More examples:
