The model of your cable modem doesn't appear to offer other than the basics. If you want to connect more than one device, you do need a router. Each device requires a unique address and you only get one such address through your modem. It's provided by your ISP. I'll take a guess and say the Cisco guy probably used a "layer 3" switch which can handle routing as well as offer more connections than your standard home router. Most of these offer 4 ports...thus, 4 connections. If you only need to connect two devices at this time, you get a router. You connect the output of the cable modem to the WAN port of the router and connect two of the LAN ports to the patch panel jacks that go to where the remote devices will be. The type of device will determine its behavior on the network Now the sequencing the power on cycle for modem and router can be an issue. Sometimes one or the other must be turned on first and the second one connected once the first is fully initialized. In my home, I need the router on first so that the modem will see it. Once the two are happily connected, most remote devices just need to be started. A PC will broadcast a request for an address. The router will see that request and provide an IP address. Any data transmitted on the network needs to know where it's going and that address is generally how it finds its way. Hope this isn't too basic or adds any more confusion.
We bought a home previously owned by a Cisco certified engineer. He had ATT U-Verse as his ISP. His connection came in through his office upstairs. He used an ethernet cable in the wall to get the signal into the office closet where there is, for want of correct terminology, a jumper board, maybe a patch panel?
The board has ethernet wiring attached on the outside of each of two vertically positioned parallel female ethernet jacks, let's number the left most 1-11 (odd), and the right most 2-12. The signal from ATT entered on jack #3. Jack #5 goes to the office in the house. #7 goes to the living/TV room at the other end of the house (more on this later). Can one add a photo to a post? If someone could steer me to the directions, I will upload a pic of the board.
The co-ax where TWC enters is near the old ATT jack in the office so I have connected one end of an ethernet cable to the output of the cable modem and the other to the same ethernet jack that he used to send his ATT signal to the jumper board. So from the jumper board in the closet, all should operate much the same way.
I first connected jacks 3 and 5 by an ethernet cable to get the signal (successfully) to the office.
I now find that if I have my office computer connected to the internet by wifi in my office, and decide to unplug the access point (to use it elsewhere) and plug my computer in directly by ethernet cable, I have to reset the modem (a Ubee DDM3521). Same if I am connected directly, unplug and then plug in the wifi access point (and the modem must be reset before the access point.)
Is this normal? Please confirm that it is necessary to reboot the modem each time something is plugged or changed around in downstream. Reason for asking is that maybe I have a problem that I am mis-diagnosing.
More questions to follow but the wording may be different as I get the answer to this and subsequent questions. TIA

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