Quoting your post above "
Depending on the modem firmware installed, the second ethernet port can be used as a second IP node (as per above) or as a Link Aggregation Port (coupled with a compatible router or computer).
If you attempt to use both ports without configuring them properly you will get connection errors on one or both of them. "
I purchased a T25 and have been having intermittent disconnects. Took it back and got a replacement. No change. Arris says they need Upstream power of +45 to +51 but both the T25s show in the +30 range. The Xfinity tech says his meter shows 5 db greater than the T25 and also says the +45 to +51 range is not achievable.
Could the configuration issues you mention be the issue? I'm using both ports on the T25. Xfinity told me I could use both because IPs are dynamically allocated (I'm beyond my competance to know what this means). How do I 'configure the ports properly'?
P. S. The Xfinity tech installed a test modem yesterday and plugged my desktop into one of the ports and my Linksys WiFi Router into the second (of 4) port.
The T25 is an eMTA modem only - it is not a router. You cannot use both ports on the T25 simultaneously unless it's for Link Aggregation, or you've bought an additional IP from Comcast.
If you want to connect multiple devices to share your internet connection, you will need a router (and only ONE router) to connect to only one of the ports on the T25, and then connect all your other devices to the router.