@section94 

Hi,

Is the ISP-provided DSL modem router physically the same unit that you used 2 years ago in the different house or is it just the same model, but a different unit?

In case the DSL modem router you use now is not the one you used previously, then you need to setup again the port forwarding rules on this new DSL modem router to have the FTP data packets forwarded to the IP address of the Archer VR600v. 

  @woozle  It is a different unit but the same model. I also suspected the ISP router might be blocking the traffic. But I never had to do any port forwarding on the old one.  Also recently discovered my ISP was blocking many ports with a "enhanced security feature" which I disabled. Never disabled that in the past when it was working and also made no difference now.

Also can someone explain this to me:

This is what the ISP router and Archer USB sharing shows with PPPoE connection type. I don't see it assigning an IP to port forward to. But the USB access addresses on the Archer seem to correctly point to pubically routable IPs (even tho they still don't work).

This is what happens with Dynamic IP connection: The Archer and my PC are assigned IPs normally but the internet USB sharing addresses all become internal IPs which are unusable for my purpose.

The WAN IPs you see in the 1st case don't match with my actual public IP as reported by sites like whatismyip which is why I post them openly. I googled and I read it may have something to do with sth called carrier-grade NAT which honestly is way beyond me.

Right now I am on Dynamic IP mode and I did this to the ISP router: 

No change. No matter what I do I can never access anything from outside the network using the public IP on any port. Could I be typing sth wrong? Lets assume traffic was completely open with no issues. What exactly would I need to input (I mean what is the correct syntax) to access a specific device from outside the network. Lets say I am on windows file explorer or filezilla on a different network and I want to connect to the USB. The LAN IP of the device I want to access is 192.168.1.15. The public IP is hypothetically 101.98.28.9. What would I need to type exactly?

  @section94 

Hi,

I am surprised that you are able to establish an Internet connection via Dynamic IP as well as PPPoE without changing the operation mode of the ISP router.

But anyway, as you have already noticed, your ISP has apparently now put you behind a carrier-grade NAT.
CGNAT uses the IP address range 100.64.0.0 - 100.127.255.255, of which your IP address 100.67.23.4 is part of.

So it looks like when you moved to another house your contract with your ISP changed and the new contract doesn't include a public IPv4 address anymore. 

To be sure about this you should also check the WAN IPv4 address of the ISP modem router. I think that modem router should have some status page that shows this information. Check if that address is also in the range 100.64.0.0 - 100.127.255.255.

But with this you won't be able to access your FTP server from the Internet.

What you could do is to contact your ISP again and ask them to put you back on a true "public" IPv4 address, like you had previously when you lived in the other house.

  @woozle 

Yea I can confirm I am behind a CGNAT. The ISP routern WAN is also in that range...

I will contact the ISP in the next days although I am afraid they will refuse to take me off the CGNAT.

One last question: If the CGNAT problem is solved, all port forwarding is done, traffic is not blocked by anything etc:

How would I reach the Archer router in dynamic IP mode where it only has a local IP? If I typed ftp://PUBLIC_IP:21 would it know to forward the request to the Archer? Or do I have to switch to PPPoE mode in order to make the USB access addresses the same as the public IP?

  @section94 

If you don't want to use PPPoE on the Archer router, then the proper port forwarding has to be active on the ISP router.

With the port forwarding you showed in your last photo the ISP router will forward an incoming connection ftp://PUBLIC_IP:21 to ftp://192.168.1.15:21.

Depending on whether the ftp connection is active mode ftp or passive mode ftp there may be additonal ports needed to be forwarded. In case it doesn't work with only port 21, then test if it works when you forward everything. (i.e WAN Port Range 0 - 65535, LAN Host Port Range 0 - 65535)

  @woozle 

Called the ISP and they took me off the CGNAT in about 30 seconds! But I asked if there there is a chance it comes back automatically at some point and they said yes. I got it working immediately after the switch with just this port forward rule above.