Maybe a part of answer here:
https://success.alienvault.com/s/article/Why-does-a-TCPdump-of-my-monitor-interface-return-ethertype-Unknown
In some environments, a physical or virtual switch can be configured to use VLANs on the SPAN ports the USM is connecting to. When using this configuration, the appliance will discard this traffic as it is unable to parse VLAN Trunking or other Bridge Protocol encapsulated traffic.
This message indicates that the network stack is not capable of reading or interpreting the traffic showing this message. As this traffic cannot be read, it will be discarded. This issue can be resolved by configuring your physical or virtual switch to pass the mirrored traffic to the monitor port as IP traffic (ethertype 0x0800).
In this context, does somebody knowss how to configure pfsense to pass the mirrored traffic to the monitor port as IP traffic (ethertype 0x0800)?
Are there some security risks to do that?
Thanks