Port Forwarding

Glad to see you're still here providing support. You've helped me immensely in the past! I do indeed still have the MB8600 and I currently have an ASUS AX-3000 for a router at this address. It's strange because this used to function perfectly fine with no issues at all. When I opened ports for whatever reason and checked them, they came back as open. For what it's worth I did also try disabling the router and windows firewalls and even temporarily using the DMZ function within the router to see if that made any difference. Even with all of that the ports were showing as closed. I did also verify my public IP and WAN IP were the same so I suppose I can assume this isn't a CGNAT issue.

In any case I did as you suggested and connected straight to the modem, bypassing my router entirely. The ports are still coming back as closed via various port checking websites. I tried again after totally disabling Windows Firewall (private, Public, and Domain) and even then they still show up as closed.

Some potentially relevant information: I recently moved to Ohio and utilize Spectrum internet there. I continue to pay for a utilize a Cox account for my parents who are the ones using the MB8600 here in Virginia. Back in Ohio, I was successfully Port Forwarding with the same make and model of router (but not the same EXACT router) and the same laptop I am using now during this visit. Therefor I am at the very least sure my laptop and firewall are not to blame for this issue.

A few more thoughts to consider,

If you connected your PC directly to the modem and the ports still show closed despite the firewall being turned off, that suggests the application isn't listening.  Your public IP would have also changed when connecting directly to the modem so make sure you aren't forgetting to account for that in your testing.

bypassing my router entirely. The ports are still coming back as closed via various port checking websites

If that is the case, then you can rule out the router, which is a good thing. Try listing the ports on your computer by Windows key + R > CMD > Netstat -ano > Left click to select the data and enter to copy it. Then paste it into wordpad and CTRL+F to find the port. 

Also, do you have any A/V other then Defender? If so, try disabling/uninstalling it.

The two ports show up in the UDP section of netstat but they are not appearing in the TCP section. I do have Avira Antivirus and have tried disabling that during these tests as well.

Have you enabled rules in your firewall for both UDP and TCP? Do you NEED both? Could be the website you are using to see if the port is open is only scanning TCP. I would suggest booting into safemode with network to rule the A/V completely out. If you have Windows 11(or if your HD is encrypted for any reason) you will need your BitLocker key.

Another thing you could try is reconnecting the router and seeing if the you can reach the port locally from another computer on your LAN. You could telnet or use a program like NMAP. Once it is confirmed open on the LAN, then you can test if you can access it via WAN.

Last, make sure you are either using static IP for the device being forwarded to, or that you have a DHCP reservation for it.