Please: the vsftpd service cannot be accessed!

Please: the vsftpd service cannot be accessed! -- Linux general technology-Linux technology and application information. For details, refer to the following section. New to me, I installed rh9 on the VM and started the vxftpd service. localhost can be logged on, But windows CMD on the host cannot be logged on.
Error message: ftp: connect: Unknown error code

In the solution for online query, the iptables firewall has been turned off, and the open port 21 command has been added in it: (The following are all successful)
Iptables-a input-p tcp -- sport 21-j ACCEPT
Iptables-a input-p tcp -- dport 21-j ACCEPT

Still unable to solve the problem.