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Question

New to cable modem and am confused

Feb 1, 2015 10:24AM PST

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

Discussion is locked

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Clarification Request
You didn't mention a router
Feb 1, 2015 10:11PM PST

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.

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Very helpful
Feb 2, 2015 4:44AM PST

Somehow I did not see Steven's reply which is extremely informative. I think he has given me enough to sort out the issue.

Two remaining questions before I get started.

1) Are there any compatibility issues between cable modems and routers? Reason for asking is that I learned that to get a signal I could not use just a router, that I had to have a specialized piece of kit, i.e. a cable modem. The house we are moving from had fiber optic and I think the "modem" part was contained in the gateway on the outside of the house that converted the fiber to copper, so I did not need a separate modem.

E.g., does DHCP need to be turned on in the router?

2) Can a switch be placed downstream from one of the four router ports if more are needed?

Many thanks, Steven

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Most home use routers are plug and play
Feb 2, 2015 9:03AM PST

You connect the WAN (wide area network) port of the router to the cable modem. That router actually creates it's own network and will give out addresses in a different range than the one provided by your ISP. You asked about DHCP. By default, these tend to come with DHCP enabled. There will be a way to access a router's web interface to make a few changes as needed but most work right out of the box. The routers IP will be your networks "gateway" address as you may encounter that term. Since most routers come with 4 ports, and because you asked, you can add additional switches by connecting these to one of the LAN (local area network) ports if you want to connect more devices such as additional PCs, network printers, wireless access points, etc. 8, 16 and 24 port switches are fairly common. You probably don't need one with more ports than are on the patch panel. If you want to go with wireless, you can get a wireless router that adds capability within a limited area of that router. To expand coverage...say to another floor...you add a wireless AP (access point) and these, when properly located, will provide a better signal to devices near them. It's really not all that complicated but, since you didn't mention the a router, I though I should ask if you already had one. Good luck.

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Answer
You would have to test it by eliminating...
Feb 1, 2015 10:58AM PST

...all of the 'monkeys in the middle'. IOW, remove the middle pieces and see if the reboot is required when you remove/relocate the AP & plug in via ethernet, when the whole shebang avoids the mess left by the engineer.

What you are experiencing isn't that unusual. Is there a particular reason you have to move around a single AP? Why not do something different elsewhere in the home with another device?

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What can I eliminate?
Feb 1, 2015 6:42PM PST

TWC comes into the home upstairs on a co-ax. I have to get the signal from that point to two different places in the home, both downstairs. The only wiring is that left by the engineer.

I think I can work through this with some help, so:

Is it normal to need to reboot a cable modem if something downstream is added or changed?

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"Is it normal to need to reboot a cable modem if something
Feb 2, 2015 4:50AM PST

"Is it normal to need to reboot a cable modem if something downstream is added or changed?"

Yes. Almost all cable modems latch onto the MAC Address of the downstream thing. So for years when I move/change the router settings I'll power off the modem, router, switch etc then bring up the modem, wait, router, wait and finally the switch (some folk only have the first two.)
Bob