2 lan interface on a single device. How to connect them both together

I am planning to setup a device with 2 Lan interface. No wan.

Both are on the same subnet.
Main reason is i want to block something from crossing between the 2 Lan interface via firewall.

Now how do i do this via software?
I tried using vlan.
each vlan has 2 port each.
i connected a utp and the 2 lans are now connected.

now is there a method to connect them both via software?
newbie question.

Layer 2 filtering is somewhat complicated because, to my knowedge, there isn't a Luci interface to make creating rules easier. If you still want to use the device as a transparent firewall, I recommend reading about nftables.

so its complicated? much easier just to make a short utp and plug them on to the different vlans?

It's easier if you have two LANs, for example: and

That way you can use the built-in firewall rule editor in Luci. Be mindful of what device is acting as your DHCP server in each LAN.

What device are we talky about!? Is it a part of a larger network? Or what exactly are you trying to adobe if you want to connect them together using this device but also want to make them separate?

im just experimenting. kinda hard to explain.
but i thinkting of having 2 interface as i can use firewall rules.
i was hoping to use a cheap openwrt device to block dhcp from crossing.

A diagram would help to understand your topology.

Also, be mindful of the XY problem when asking questions.

Please do the best you can to explain your general ideas/plans. For example (just making this up based on my own network):

  • I own/control the network -- it is a home network and I can control all devices.
  • I want to use a single router (hardware) to setup multiple networks.
  • The networks should be isolated: trusted LAN, guest, IoT.
  • I would like devices on the trusted LAN to be able to initiate connections with devices on the other networks. Those devices should be able to respond, but not initiate connections to the trusted LAN or between each other.
  • I have a smart switch and want to share as much of the physical infrastructure as I can (or conversely, maybe the plan is to have each network on its own physical ethernet port from the router).

Providing details about your ideas like this will help ensure you get relevant advice. The more detailed, the better.

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