Extending LAN to second physical ethernet port

[cellulosa]

hi there, is it possible to setup a physical eth interface to be an “extension” of another?

I have a device that for some unknown reason doesn’t work when connected to my PoE switch, but does on an ancient router (support mentions it could be related to signal fluctuations or speed, I’m trying to figuring it out).
Anyway, since I have additional physical ports on the VyOS machine, I thought I could use that.

However, since I’d only ever connect a single device, I wonder if there is a simple way to do so without adding too much config complexity (e.g. VLAN or bridge interface)? Is it possible? e.g. simply setting a fixed address to the interface and then including eth2 amongst the LAN interface group for firewalling?

Here’s a visual reference of my topology to help:

    ┌─────┐   eth0┌─────┐eth1   ┌────────────┐    ┌────┐
    │ ISP ├───────┤VyOS ├───────┤ PoE Switch ├────┤PCs │
    └─────┘       └──┬──┘       └────────────┘    └────┘
                     │eth2
                     │          ┌──────┐
                     └──────────┤Device│
                                └──────┘

[tjh]

Your only real choice here is to use a bridge.

[cellulosa]

I created a br0 bridge with member interfaces eth1 and eth2 and changed all eth1 references of my settings to br0. Works like a charm, thank you!

One question though, is there anything else I should be considering? e.g. set interfaces bridge br0 stp or any other setting to make the bridge interface work smoothly?

[cellulosa]

Is there a way to advertise the client of eth2 to the PoE switch attache on eth1? Since they’re all part of the same bridge interface?

[tjh]

I don’t understand what you’re asking. There should be no reason that your bridge doesn’t behave as a normal bridge. What’s not working?

[cellulosa]

Apologies for my ill-put or more likely silly question due to my lack of expertise.

What I mean is, I cannot see the device connected to the eth2 port on the PoE interface which is connected to eth1. I guess that’s not possible because that’s “one level up”? And so the PoE cannot see it and can only see the devices connected to itself?