I'm trying to figure out the easiest way to switch between two different WAN interface protocols (DHCP and PPPoE), but I'm not sure what approach might work or if there's a better solution.
Background:
My previous ISP-provided router had a “modem mode” that acted as a DHCP server, so I could connect my main OpenWRT router’s WAN port to it as a DHCP client.
As a manual backup, I have a “Pi-modem” - a Pi running OpenWRT that connects to my phone in wireless hotspot mode to use its data connection, which I could just plug in to the main router’s WAN port instead of the ISP modem without needing any configuration changes.
This solution worked perfectly for my needs.
Problem:
I have recently switched to FTTP, and my new provider requires using PPPoE with credentials to connect. I've changed the main router’s WAN port to PPPoE and it works fine, but this means I can no longer just plug my “Pi-modem” into the WAN port instead as I did before.
This is only for rare emergencies, so I don't want to set up mwan3 or have a dedicated port on the main router.
Is it possible to run a PPPoE server and DHCP server on one port without VLANs? If so, I could reconfigure the “Pi-modem” with PPPoE with the same credentials as my ISP, but still connect it directly to a PC as needed for configuration etc.
If not, is there a way to have two “wan” interfaces on the main OpenWRT router for the same port - one DHCP, the other PPPoE? If both could be enabled at once that'd be ideal, but manually disabling one and enabling the other in luci would be workable. I don’t believe I can use one interface and change protocol, as it would lose the PPPoE credentials when switched to DHCP.
Maybe there is a better approach entirely, without needing mwan3 or other complex setup on the main router?