libreCMC/docs/Bridge_Mode.md

Bridge Mode

A common feature of COTS Wi-Fi routers is to be able to set the router to bridge mode, where the devices stops acting like an IP router (layer 3) and starts acting like an ethernet switch (layer 2). LibreCMC does not actually have a bridge mode, but the same effect is achievable with two easy steps.

1. Add the WAN ethernet port to the LAN bridge interface
2. Set the DHCP server to ignore the LAN interface

Adjust the LAN bridge interface

Go to the Network >> Interfaces page and press the EDIT button next to the LAN Network. Select the Physical Settings tab.

Place a checkmark in the box for the "eth0" interface for wan and wan6. (I suppose the interface name might vary amongst different routers.)

You can also check the box for Enable STP if desired. There doesn't seem to be any downside from this, though I suppose it would use a little more CPU cycles and memory. STP is a protocol intended to prevent infinite communication loops from forming in a network of layer 2 switches.

Adjust DHCP server settings

On the same page, scroll down a little to the DHCP Server section. In the General Setup tab, check the "Ignore interface" box.

Save and apply your changes.

Communicating with LibreCMC in "bridge mode"

Now that the DHCP server is turned off, the next time you connect to the libreCMC device, you will not be able to communicate with it. You must set your connecting device manually to be on the same subnet. Since the default libreCMC LAN IP address is 192.168.10.1/24, it should work to set your connecting device to IP address 192.168.10.2/24.On Gnu/Linux systems, the command is usually ip addr add 192.168.10.2/24 dev eth0 or dev wlan0 if connecting wirelessly.

Alternatively, you may set the libreCMC device to receive an IP address from another DHCP server on your network: go to back to the Network >> Interfaces page, press the EDIT button again next to the LAN Network, select the General Setup tab, and switch the Protocol from "Static address" to "DHCP client". (It seems that in LibreCMC, bridging the LAN interface to the WAN port disables the operation of the DHCP client on the WAN interface.) Of course, if you do this, be sure that your DHCP server has reserved a memorable IP address for the LibreCMC device's MAC address, so you don't have trouble finding it.

Adjusting the firewall...?

To make a more consistent look in the your LibreCMC interface, you could go into Network >> Firewall and do things like deleting WAN zones or disabling NAT masquerading. But since the ports are bridged, it isn't necessary, and it will only make it more work to switch back out of "bridge mode" if you want to later.