One of my computer repair clients called one afternoon stating their internet is up and down on their Linux Mint laptop. A service call was made. Upon arrival my client turned on the HP laptop. Linux mint started and displayed the desktop. I checked the internet connection and it was blinking on the ethernet port to the comcast router. Firefox was started and it connected to my two websites without any problems. The Linux update app had 19 linux updates which got installed.
My client tried his banking site and it was back to not working. I looked at firefox and found the system proxy settings were enabled. Thinking I had found the issue, I disabled it. This made no difference so I was back to square one!
I moved the ethernet cable on the Xfinity router from port 4 to 1 to see if hardware is the culprit. My client tested his banking site and it was much faster like it was earlier. Port 4 must have a connectivity problem which means the Xfinity router may be failing.