Use ISP modem as PPPoE and as switch at the same time

Hi All!

Long time lurker, mainly because the time I started actively using OpenWRT coincided with profound changes in the way I live. Now I'm going full-OpenWRT. I already have a Linksys WRT1200ac with OpenWRT, and looking into adding a Banana Pi R3/R64. Wanted to ask for some advice/guidance to plan ahead though. I did search old topics, but have yet to find anything like my question.

I have an ADSL modem with 4 LAN ports and a DSL port, currently acting as the main gateway. It does support VLANs, but doesn't have enough configuration possibilities especially with respect to IPv6. I want to manage my home LAN through OpenWRT. However, there are multiple devices near the modem, so I also want to keep using its LAN ports and avoid adding yet another network device.

The plan is:

  • Modem Port 1 to OpenWRT Router WAN, with VLAN0. Not other devices in this VLAN.
  • Modem Port 2 to OpenWRT Router LAN, with VLAN1. All devices at home will live in this VLAN.
  • Modem Ports 3 and 4 connect to the TV and any other devices (via a dumb 100Mbps switch or something). This VLAN is controlled by the OpenWRT router, DHCP and all. So essentially the ports 2 through 4 will work as a switch for OpenWRT LAN side.

Do you think this would work? I did draw something to better explain but I'm so new to the forums that I haven't found how to add images yet. :slight_smile: Thanks in advance for the ideas!

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Other than that the part where you assign ports 2-4 to the OpenWrt lan might complicate things. I am not sure if the modem can handle such a scenario where it will have some ports of its own managed by another router. It would be possible to have devices isolated:

internet - modem - LAN1 - wan - OpenWrt - lan - hosts
                 - LAN2-4 isolated hosts
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Thanks for the reply! Can I offer you a virtual coffee, for the first reply to my first question? :slight_smile:

The isolated hosts scenario defeats my "all internal hosts IPv6 DCHP" scenario, plus there are servers (including a piHole) at the OpenWRT router LAN side. :slight_smile:

And thanks for the tip regarding the drawing. Here it is!

Then it would make more sense to have all the lan hosts connected on OpenWrt.
Depending on the protocol used to get your public address, you could make the modem just a dummy bridge and terminate pppoe on the OpenWrt.
Then it may be possible to achieve your goal as depicted.

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