FTP in passive mode cannot connect to the internal server through the NAT server

Hello everyone,

The topology is as follows:

Server——USG——ISP——PC1

IP deployment:

Server: 192.168.1.2

USG(trust): 192.168.1.1

USG(untrust): 10.1.1.1

PC 1 is a dial-up user.

NAT configurations on the USG are as follows:

nat server protocol tcp global 10.1.1.1 ftp inside 192.168.1.1 ftp

acl 2000

rule permit

firewall interzone trust untrust

nat outbound 2000 interface e0/0/0

The firewall can access the server in active mode, but cannot access the server in passive mode.

Please tell me why. And how to solve this problem.

Thank you!