Let me describe the bizarre situation here in simple terms.

  • I need to get an Ethernet connection from the network closet to the garage TV.
  • My main router is an OpenWRT Linksys wrt32x which has 5 gigabit Ethernet ports (1 WAN, 4 LAN; although this can be reconfigured for 2 WANs if we want for whatever reason), a USB 2.0 port, and a USB 3.0/eSATA port, both of which I can do whatever USB shenanigans I want (I own a rare USB-A male to USB-A male data link cable, and I've heard of running PPP over serial? if that's at all relevant).
  • There is a single data line (CATV over Coax) that runs directly from the closet to the garage. This coax line is marked "DIRECTV RJ-6 75 Ohm High-Performance 3.0 GHz," which is kind of weird because we've never used DIRECTV on this line notwithstanding.
  • The CATV signal isn't that important so replacing it with a data-only line is A-OK (but my ISP runs both on the same wire so I assume it's possible to do that myself as well).
  • I have a DOCSIS 3.0 cable modem/router combo, the Cisco DPC3825, that as of now is being used just as a 4-port gigabit Ethernet switch. It has 4 gigabit Ethernet, 1 coax, and 1 USB port. This one doesn't have OpenWRT support unfortunately.
  • The most obvious solution, wireless, is not usable because it's what we already have-- it hasn't been working at all. Given how terrible the speeds on even 802.11ac with the device 15 yards away have been I think there's some sort of interference in the garage due to some electrical equipment, but I'm no expert. It could also be that the access point is shitty, but regardless I prefer static wired setups to wireless ones if possible.
  • I want to run a DOCSIS signal on this coax wire, over which the LAN (Link layer Ethernet/PPP/etc bridge OR network layer IP tunnel are both good) connection will run, that can be modem'd by the DPC3825. Essentially I want to be both the "customer" (garage) and the "ISP" (closet) at the same time.
  • The topology of the link I'd like to achieve is this:
|                          |              |                                                                   |
Router <--Ethernet--> [???] <--Coaxial-Line--> DOCSIS 3.1 Modem <--Ethernet--> Switch <--Ethernet--> Garage TV

Basically all I'm looking for is the [???] listed above. I've spent a while trying to find documentation on using DOCSIS for a LAN but nothing's turned up. It's not typical to run what's typically used an ISP's protocol WAN-LAN connection as a LAN-LAN connection, but I've actually done this kind of thing before, only with DSL/PPPoE instead, and it worked despite being super weird (all I did then was use OpenWRT as a PPPoE server and attached an old DSL modem). I want to take advantage of the modem I already own-- yes, MoCA/G.hn could solve this problem easy, but devices for them're quite expensive. Is it practical to emulate the PPPoATMoDOCSIS that my ISP uses?

I've no preference as to whether it's a solution involving layer 2 (Ethernet/PPP/etc) over DOCSIS or layer 3 (IP) over DOCSIS: just as long as I can get to my local subnet from both ends, it'll work; and since I've not been able to find anything about a sort of system like this, I'll try to try out what I can just for future reference if nothing else.

  • 1
    Two issues here: First of all, this is likely off-topic for Home Improvement. Second of all, DOCSIS is not designed for your intended use and you don't have the correct equipment to implement what you need to make it work. Your cable modem is a DOCSIS client box only. There is no server side and that means you don't have a working DOCSIS system. See this link: thegeekstuff.com/2012/05/docsis-introduction – jwh20 Mar 25 at 18:49
  • It's also really difficult for me to figure out what root issue you're trying to solve. Perhaps if you simplified your question, leaving out everything superfluous and describe the situation it would help. – jwh20 Mar 25 at 18:50
  • All right, what I'm trying to say is "I want to get my garage Apple TV connected, and the only wire to it is coax from the network. Can I run a connection over that?" I've tried using wireless but for whatever reason what's been really terrible at holding a connection, so this (and powerline Ethernet I guess) were what I came up with. – BoomBoomPowe Mar 25 at 19:26
  • Bottom line is that your RG-6 is 75 Ohm coax which is NOT what is used for the old Ethernet Coax solution which uses 50 Ohm coax. For a short run you could possibly get away with it but I'd expect issues. What you need are TWO RJ-45 (i.e. 10Base-T) to 10Base-2 transceivers that would convert from your wired LAN to the coax and then from the coax to wired LAN. Then you could plug in your Apple TV or add a WiFi AP if needed there. You'll be spending a lot of money for all this and you're probably better off just running some CAT6 to the garage. – jwh20 Mar 25 at 20:05
  • Ahh, so it's literally a different cable. I'll stick to using coax for basic cable since running cat5e or even cat6 to the garage wouldn't be very expensive given my circumstances; thanks for the information. – BoomBoomPowe Mar 28 at 19:38

You need an ethernet-over-coax device for RG-6 cable.

A slightly surprising source of these is CCTV suppliers, as there is a lot of analogue CCTV wiring out there, and people want to upgrade to higher resolution IP CCTV, without running new cable. Therefore, converters to run Ethernet over Coax are available.


VHW-HW HIGHWIRE Ethernet over coax converter (2 required per link) 100BaseT up to 350m (1150ft) full-rate over RG-6


One supplier


There is also a possible hack solution - connect wifi antennae connectors directly to the co-ax cable.

There are some problems with this plan. WiFi is 50 Ohms, TV coax cable is 75 Ohms. Only one MIMO channel will be available meaning the maximum theoretical bandwidth will be 433 Mbps. WiFi is also at much higher frequencies than what coax is designed for.

With two WiFi antenna to coax adapters, [Tobias] simply connected the coax directly to a router set up to bridge Ethernet over WiFi. The entire thing worked, although testing showed it was only getting about 60 Mbps of throughput.


| improve this answer | |
  • That "use the coax for a wifi antenna" hack is pure win. a 10Base2-10BaseT adapter. – Harper - Reinstate Monica Mar 26 at 2:45
  • Sounds all right; I was just curious if there was a different potential solution that might be less expensive lol. I'll have to try out the wifi antenna straight to coax thing though, worth a shot. – BoomBoomPowe Mar 28 at 19:40

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