Meraki MX Warm Spare LAN Port state

[PabloR]

Can the LAN Port of Meraki MX HA Warm Spare forward traffic if there is a connected device behind them? 

I need to connect a second firewall as a standby in HA mode active/standby behind the MX warm spare, and I need to confirm if the LAN Port is forwarding traffic while Meraki MX warm Spare is in a standby state.

[PhilipDAth]

It forwards packets in the same VLAN at layer 2.  However, the layer 3 routing engine is only running on the "active" MX.

[RomanMD]

As I understand it, you have a FW cluster behind an MX cluster.

In that scenario, it seems that you need to connect both firewalls to both MX'es (MX cluster does not operate in Active-Active scenario for simple routing purposes), otherwise, if your primary FW will crash while the primary MX will still be up nothing - good will happen.