I use Xfinity/Comcast internet at home and use their Cisco gateway. I also have an Amcrest DVR security camera set up that I can access from an outside computer if I use port forwarding on my Xfinity router. For the past few days, the port fowarding only works briefly, immediately after I restart the router/modem. After a few minutes, the designated ports close and I have to restart the modem again in order for the port forwarding to work and for the ports to be open so the security camera is accessible over the internet.

I have no problems accessing the cameras via the phone (P2P) set up because it doesn't use port forwarding. Why would the port forwarding work, then stop working and only work again if I re-start the modem?

Just to be clear, if I re-start the modem (remotely using a computer attached to the internet), I can use an open port checker to confirm that the designated port (18295 in this case) is open. I can then log in to my security cameras. Within 5 minutes, if I check the port again, it will be closed and if I try to change the view or switch to another camera, the connection is gone and I won't be able to log in again due to "The DNS server might be having problems. Error Code: INET_E_RESOURCE_NOT_FOUND" because the port is closed. If I re-start the modem/router, the port will open again and I can log in to the camera for a few minutes until it closes again.

Any ideas? Could this be a problem with the modem/router? Or is this likely something on the Comcast/Xfinity side? Is calling technical support likely to be worth the effort of explaining this to numerous call center operators before finding someone who can help?

Are you sure the public IP address that Comcast is leasing your modem, isn't changing?

And do you have some kind of dynamic dns client running on your router?

The IP address of the LAN stays the same as well as the relative IP address of the security cameras on the LAN (cameras are always 10.0.0.219).

I'm not sure about the dynamic DNS - the router has Comcast's DNS servers identifed as primary and secondary (75.75.75.75 and 75.75.76.76). The amcrest NVR has googles DNS servers disignated. This set up was working fine until Comcast/Xfinity rolled out advanced firewall security for everyone a couple weeks ago, I believe. Does the DNS setting cause the forwarded ports to close? Because it works fine right after a modem reset, then port forwarding seems to stop working until it's rebooted again.

SuperdutyAg85 said:

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The IP address of the LAN stays the same as well as the relative IP address of the security cameras on the LAN (cameras are always 10.0.0.219).

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Those IPs are your private IPs and likely wouldn't change.

I'm suspicious of your public IP changing causing you to not be able to connect back, depending on how you connect back to your home. From inside your network, you can go here periodically to see if your public IP is changing.

https://whatismyipaddress.com/

What DNS domain name or client are you using to connect back to your cameras while not on your home network?

So you're using Comcast's router as well? If they introduced some firewall change to it, it could have a bug and screw up the port forwarding potentially.

I'm using the DNS setup/name specified in the Amcrest instructions (http://assignedname.amcrestddns.com:port#) with port# being the port being forwarded. The whole problem is that this port (18295) is not being left open for access. Immediately after rebooting the modem, I can verify it's open using https://www.yougetsignal.com/tools/open-ports/. Then I can log into the cameras. A few minutes later, this port closes and I can no longer access the cameras unless I reboot the modem again.

The IP address of my home network (or the relative IP address of the cameras on the network) doesn't seem to be changing and neither is the IP address of the computer I'm using to access it.