Thx. So, if I'm right, we agree that TP-Link router blocks 445 port forward in all forwarding rules (445=>445 and 4445=>445 as well), not the ISP. Why does it block??? By default, nothing is...

If port forward 4445 => 445 worked on the router, OTCP should show port 4445 opened, independently from the ISP

Sure. But the ISP does not block: a Huawei HG8143A5 router (before my current TP-Link router) did forward the 445. Now: 4445 => 445 (SMB): OTCP shows closed 4445 => 1058, 2049 (NFS): OTCP shows...

I've got the same problem. Just I'd like to port forward the SMB (445 port). Doesn't work. There is useful page Open Port Check Tool - Test Port Forwarding on Your Router, (OPCT), where you can check...