“unknown devices” connecting via ethernet to XB8 gateway SOLVED - caused by “known ethernet devices” generating additional MAC addresses

First, please note this issue has been solved. (See below for Solution and Cause)

This post is intended as an FYI FAQ and may not exactly match your situation. But, I encourage you to read ahead if you find similar issues with unknown devices connecting via Ethernet on your home network. 

The issue:

We recently upgraded to an XB8 gateway and noticed in the Xfinity App several unidentified devices connecting via Ethernet.  This was true after turning on Advanced Security and after accounting for, and assigning, all devices to users in the Xfinity App. In our case, the Xfinity App would identify these extra ethernet connecting, unknown devices, as a “Roku Device” and “unknown apple device”.

The Known:

We accounted for all Wifi and Ethernet connected devices by verifying their MAC addresses in the Xfinity App. 

We did not own a Roku.

We didn’t have any unaccounted for wired Apple devices.

We had a setup of XB8 gateway-> 8port 1Gb dumb switch (no self MAC address)-> to 4 ethernet connected devices.

All other known devices connected via WiFi.

First Assumptions and attempts:

Initially, we guessed that a neighbor was able to inadvertently connect to our XB8 gateway “via ethernet” as they were on the local Xfinity Node with us.  How? We assumed that either their residence didn’t have a proper MoCA filter or ours didn’t - possibly both. If either scenario was true, then others in the local node could see neighboring devices on other gateways, connecting or pausing devices with the Xfinity App. Although we paused these unknown devices, they never disconnected and therefore could not be deleted from the Xfinity App.

Xfinity Troubleshooting begins:

At two different times Xfinity sent techs out.

The first looked at the DEMARC box at our residence. This is the first point where cable from the street connects to cable in the house. If properly installed, the connection between these two cables will have a Point of Entry (POE) MoCA filter. This prevents our network from being seen from outside our home on the local node. All residences should have a MoCA filter. And indeed ours did. But the tech replaced it with a new one just in case.

This didn’t get rid of the unknown ethernet connections. Even with hard resets of the XB8 gateway. 

So, when a second tech came out he installed a second filter directly to the back of the XB8 Gateway. This also didn’t work, even after additional restarts of the gateway. 

Final Troubleshooting:

We decided to go back and re-trace our steps. 

We disconnected the switch and all Ethernet connected devices from the XB8.

Bingo! All unknown ethernet devices disconnected!

So, we knew from this that the issue wasn’t from neighbors connecting to us as the MoCA filters were working. Instead, an ethernet connected device on our network was causing the issue. We confirmed this when removing the extra MoCA filter on the cable modem, but leaving the DEMARC MoCA filter in place. No further unknown ethernet connections. Yea!

Our Solution and Cause:  

After reconnecting the network switch, and each ethernet device one at a time, no unknowns appeared in the Xfinity App until we reconnected our Ooma Telo.

When connected to our network, after the switch, it generated 3 different MAC addresses: its own default and two additional. By adjusting an internal menu setting on the Ooma Telo,  to use only its built-in MAC address instead of Automatically creating a MAC address, the issue was resolved. It also worked to just leave it disconnected LOL.

General Troubleshooting Advice for unknown ethernet devices:

If you encounter similar unknown ethernet devices on your network:

1) Ensure that you have a MoCA Filter installed and properly working between your network and the local network node. Contact Xfinity for assistance if you’re unsure how to do this.

2) While using the Xfinity App, verify all connected devices against the MAC address for each device, and make your life easier by creating users and assigning devices to these users. Extra devices will be easier to spot when unassigned in the Xfinity App. The app will also alert you to new device connections.

 

3) Disconnect and reconnect all ethernet connected devices to your Gateway, one by one, to see if doing this suddenly has multiple devices connect at the same time in the Xfinity App. If this happens you’ve identified the source of the unknown device. Check that device’s documentation for options to prevent the generation of additional MAC addresses and only use the default MAC address.