Networking – How to Deal with Incoming Port Blocking by ISP

firewallispnetworkingport-forwardingrouter

First post here.

I've recently moved into an area where there's only one ISP. I had a file server running on my Windows based machine (FileRun) which was working seamlessly. I had configured a port forwarding on my router for port 8000 and configured my Windows Firewall to accept incoming connections from this port. Everything worked.

Ever since I moved to the new ISP, my file server has stopped working. I did some fidgeting and found out all my incoming ports are blocked. I rechecked my firewall and router settings, all seems OK. So I started pointed finger to my ISP that it might be blocking all incomings.

I've written a detailed email to their technical support and this is what they reply:

Kindly be informed that services are connected on GPON platform where
broadband session is normally terminated on ONT & devices will get
private IP’s & not public IP. If you want public IP on your device
than you should purchase static IP from DU(we will configure port4 of
the ONT in Bridge mode ).

This is too technical for me. I merely asked them if they were blocking the incoming ports or not, and that my server stopped working after I subscribed their service.

Can anyone help interpret the ISP's response as to what it means? I know they're forcing me to purchase their static IP service, but thats not my problem. I just need an incoming port. I use DuckDNS to resolve my IP.

Thanks

Best Answer

What they have done is that they have set up Carrier Grade NAT (CGN). Simply explained you are behind a big router shared with all the other subscribers.

If they were to open e.g. port 8000 for you, they would have to forward the port from the one external IP you all share to your IP, and this could not be done for others - for that reason there are no open ports.

If you get a static IP you would no longer be behind the CGN, and you could manage ports as you want to.

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