Can MoCA be used behind a wired router?

Question

We have Comcast cable internet, and we want to connect two devices: one WiFi router, and one PC via a wired connection. We have these all set up in the same room and it basically works:

wall --coax--> cable modem --cat5--> (WAN) wifi router (LAN) --cat5--> PC

(The modem is an Arris TM822G DOCSIS 3.0 model that also provides phone service).

Unfortunately, though, the wifi signal doesn't reach to the back of the house. We do have another cable outlet at that end, though, so we're contemplating using MoCA to run ethernet over the cable setup. We got an Actiontec ECB2500CK01 two-adaptor MoCA kit and, following the instructions and some internet forum advice, set it up as follows:

wall #1 --coax--> splitter --coax--> cable modem <-------
                          ^                             |
                          |                            cat5
                          |                             |
                          ---coax--- MoCA adaptor #1 <---

(This is already confusing to somebody who's only used to twisted-pair, as both the WAN connection to the cable modem and the LAN connection from the MoCA adaptor are apparently supposed to travel over the same coax cable, but I guess that's the magic of RF.)

Theoretically, in the other room we would then set up:

wall #2 --coax--> MoCA adaptor #2 --cat5--> wifi router

However, before getting this far, we realized there was a problem: neither the cable modem nor MoCA adaptor #1 have a free Ethernet port, so there's no place to plug in the wired PC.

Now, there is a third cable outlet elsewhere in the house, so theoretically we could get a third MoCA adaptor and plug both it and the cable modem into that outlet, while using MoCA adaptor #1 just to hook up the PC. However, that's another $80-$100 down the drain plus it seems stupid.

On the other hand, I might have a wired router at the bottom of a box somewhere, in which case this seems like it might work, in theory:

wall #1 --coax--> splitter --coax--> cable modem <------
                          ^                            |
                          |                           cat5
                          |                            |
                          |                          (WAN)
                          |                       wired router
                          |                          (LAN) --cat5--> PC
                          |                            |
                          |                           cat5
                          |                            |
                          ---coax--- MoCA adaptor #1 <--

Should this work? Is the MoCA adaptor smart enough to just route LAN traffic? Am I likely to run into trouble with Comcast expecting the router to have a certain MAC address, or any of that sort of nonsense? If I'd be better off just running 50' of cat5 under the floorboards, I'd rather find that out before I go any farther down the MoCA route.

Solution 1

MoCA bridges are an Ethernet extender

We got a two-adaptor MoCA kit

The adapter you purchased is a 'bridge' type adapter, in which case the concept is that of a fancy media converter. The Ethernet signal is simply encapsulated for MoCA and sent through the coaxial connection, and decapsulated on the other end back to Ethernet. Ultimately, consider it a long Ethernet cable.

Wiring your house

It sounds like the Comcast supplied cable modem does not have a built-in network switch and only has a single Ethernet port on it. This means you must use a router to expand the number of devices that can use that connection, as otherwise Comcast will only deliver a single network address to the first device you connect.

Modern 'integrated' WiFi routers have this routing capability built-in, so you can use the WiFi router you already have, or the wired-only router you already have for this purpose.

The network diagram will then be:

WALL -- Splitter -- Coax|MODEM|Ethernet -- WAN|        |LAN1 -- PC
            |                                 | Router |LAN2
            |                                 |        |LAN3
            |                                 |        |LAN4 -- -|
            |                                                    |
            |- - -- Coax|MOCA|Ethernet - - - - - - - - - - - - - |

And in the other room, of course:

WALL -- Coax|MOCA|Ethernet -- Device

What you can do to test this with the equipment you already have is set it up in the above configuration and see if that PC in the other room can reliably connect to the internet. If you can, good! My speculation on DOCSIS vs MoCA is wrong. If you cannot, then you might look into running Ethernet alongside your existing coaxial cable connections. That's a discussion best held in another question, but there are many examples and tutorials available online on how to do such a setup.

MoCA on DOCSIS could be an issue

The cable modem is getting it's upstream connection via DOCSIS as (to my knowledge) Comcast does not use MoCA for their WAN. If you can supply the model number and manufacturer of the modem I can confirm this. This means you must have that cable modem attached to the same connection as the TVs in your house. The problem this introduces for your proposed setup is that MoCA requires similar communication bands that DOCSIS uses, and your Cable TV will be sitting using. This may either reduce the MoCA connection's bandwidth or will cause interference on the DOCSIS internet connection and/or cable TV. Likely it will cause issues with all three.

Solution 2

You need to understand that your first MoCA bridge device is converting ethernet into MoCA (ethernet over coax) and the second MoCA bridge device is converting coax back to ethernet. So, you go from wall coax to modem (DOCSIS), modem to router WAN, router LAN to MoCA bridge, MoCA bridge to coax splitter, splitter to coax, coax (MoCA ethernet) to second MoCa bridge device, STB or other MoCA device, and MoCa bridge device ethernet out to ethernet in of WAP, for instance. I hope this helps.

Comments

[Frank Thomas]

I've not looked into MoCa before tonight, but it really doesn't seem customer focused (focuses on cable providers). I'm wondering if powerline isn't the better choice for your constraints, though I would set up a wireless bridge and AP about halfway through the house myself, but that would cost a little more.

[David Moles]

Wireless bridge was my first thought too, but this piece convinced me it was worth trying MoCA first. A linked review of powerline adapters suggested that they probably wouldn't work well with our breakers.

[Spiff]

MoCA, as a specification/technology, has the ability to work in different RF bands in order to avoid interfering with the bands that may already be in use on the same coax cable for cable or satellite TV (or DOCSIS cable modem internet) service. But individual MoCA products may not support all of the different bands that the MoCA spec allows for. North American cable TV operators generally use from 5MHz - 1002MHz (~1 GHz). What MoCA calls the "D" band starts at 1125MHz, so that's the band recommended for stuff that needs to coexist with cable TV and DOCSIS service.

[Spiff]

That said, some DOCSIS cable modems and cable TV set-top boxes that weren't designed with MoCA in mind may be thrown off by powerful MoCA signals on the same coax, even when MoCA is operating in the D band well above 1GHz. So sometimes you need to connect a MoCA filter in front of your cable modem or set-top box to keep MoCA from hurting your DOCSIS speed/stability or your cable TV reception.

[Cellivar]

Very good points and good information. The reason I mentioned it was that the lower grade consumer stuff you find on the market tends to be a little more fast and loose with specifications these days. It'll work, but it'll work mostly. This is why I suggested testing it before bringing up the compatibility issues, we can speculate all day but what matters is what people are actually capable of getting working.

[David Moles]

I've updated the question with names/model numbers and links for the router and the MoCA adaptors.

[David Moles]

FWIW, since I discovered I don't actually have that old wired router lying around, we're looking at just wiring the house for ethernet.

[Cellivar]

My speculation was correct, the device is a simple MoCA bridge device and the cable modem is just that, a DOCSIS cable modem. Wiring the house will end up being a better long term solution and can add to your home's resale value if that's in your future plans. I hope I was able to help, and would appreciate you marking the answer as accepted.