In the article he makes a VLAN, and has a VLAN-aware switch so that works fine. My switch is not managed or VLAN-aware, so that's not an option (right? It's a [switch model here]).
I was thinking something a bit... different to solve my problem. "Just" expose the TV box directly to the modem, as if it was hooked up to a switch directly to the modem. I had some basic ideas about how to go about this:
Put the WAN interface in promiscuous mode, and drop all packets not for actual interface MAC and the TV box's MAC (ebtables)
Then redirect (also with ebtables) everything that's for the modem from the TV box and vice versa with something like redirect -j DNAT --to-destination [modem mac] (I really don't know how to work with ebtables, this is a big part of why I'm posting this)
Please tell me why this is a terrible solution and/or help me get to the actual commands I would need to make this work, but I really need this or whatever else to work (there must be a simpler solution for this) and it wouldn't be possible to run more than just the one Ethernet cable to the TV.
You do not want to enable promiscuous mode on the WAN - this is a security issue.
this probably won't work, as I'm guessing that the IPTV service is either using VLANs (on the service side) or is doing something special with the DHCP requests to get an appropriate IP from the ISP.
A basic smart switch (that supports VLANs) can be pretty cheap -- this Netgear unit is $17 USD from Amazon. It is cheap enough that it just isn't worth messing around with trying to hack your own solution.