Is there a way to test if port is being blocked by ISP rather than something being wrong with router/firewall settings? I am trying to use DVR in my house but ports are beeingg closed no matter what I do. I set router port forwarding and test ports and they are still closed. I am unsure if i am doing aomething wrong or this is ISP issue.
Your ISP might be blocking some ports, like typical filesharing ports, or Port 80/443.
One reason to block port 80/443 might be to block access to wrong configured routers which open their web interface to the public.
Another reason might be, your ISP does not want you to use your soho internet connection to host a website.
You can try a random port, just make the source port of your forwaring 1234, and the destination port 80/443.
Another possibility is, that your internet access is also behind another NAT router at the ISP, because it might have run out of IPv4 Adresses, as they are very rare today. This allows the ISP to run multiple users with one public ip.
You can check the ISP ports blocking on this page