How to make an FTP server available behind NAT + Cloud Mikrotik and behind a NAT provider with a dynamic IP?

Question

NAS

Such situation.
There is an Internet provider with the issuance of dynamic ip-addresses and a connection via PPPoE.
There is a Mikrotik router with the IP / Cloud service enabled on it.
There is a NAS Dlink327 with ftp enabled on it.
Task: to make available the ftp-server from the Internet.
My course of action is this. First, I create a rule in IP / Firewall / NAT that forwards for external connections (chain: dstnat, in.interface: my_pppoe, action: netmap) port 20021 to port 21 of the NAS.
After that, a connection is created from the external Internet (client: Filezilla, host: xxx.sn.mynetname.net, port: 20021) :

Status: Connecting to my_ip:21...
Status: Connected, waiting for prompt...
Error: Unable to connect to server

However, since it is in passive mode, and my client works in it, the client still needs to connect, and in order to transfer data on the port that the server from the range 55536-55663 indicates to it, the connection is not fully established, as far as I understand.
No problem, I'm trying to create a rule for incoming connections with the settings chain: dstnat, in.interface: my_pppoe, action: netmap and open ports 55536-55663, but in the end I get the same log as above.
What to do, how to be? I tried to read similar topics on the Internet, but I did not find the answer to my question. I tried to check the "Report external IP in PASV mode" checkbox in the FTP server and specify my dynamic ip there, which is obtained from the provider, but this did not help either, and this is hardly the right way, since it will change at any time and Changing it every time in the settings is not an option.

Answer 1

and here I am with a stupid question a little off topic. why actually ftp?

Answer 2

if mikrotik has a white dynamic ip, then just open one more minimum port - 20.
Port / ID: 21 / TCP for commands, 20 / TCP for data, 49152-65534 / TCP dynamically
more here: https://ru.wikipedia. org/wiki/FTP
if you are sitting at the provider behind nat - either VPN, or buy a white IP address from the provider (static or not - decide for yourself with them).