2nd NIC for Port Monitoring

[darkrevenant]

I have ProxMox (free) installed on a system of mine. The main NIC has an IP of 192.168.86.222 and is connected to an HP switch, which in turn is connected to one of my Google mesh routers.
I have a USB 1gb NIC that I want to plug into the system, set it as a second NIC but on the same lan and use it for port mirroring/monitoring.
One of the VMs installed on my proxmox is security onion.
I need help in setting up the 2nd NIC for port mirroring on this device for my SO VM.
I had tried creating a 2nd Linux bridge and assign the 2nd nic to that vmbr1 (with an IP of .111) but it does not allow me to add the same gateway as it says it is already in use by vmbr0 (which the primary NIC is attached to).
Additionally, I have STP enabled on my HP switch except for the 2nd port (which is used for port monitoring of the mirrored port), but the minute I input my 2nd nic, it creates a routing loop and my network goes down.
Help, please.

 

[LnxBil]

Port mirroring and monitoring is best used on your switch or if you use Open vSwitch instead of linux bridges. Open vSwitch also has out-of-the-box support for it.

 

[darkrevenant]

I'm using it on my switch but for some odd reason, it creates a routing loop. Still can't figure out how to stop that part.
I read the link you sent, I guess I can use it along with the switch correct?
The switch on port 2 is the monitored port, in which the proxmox open vswitch I would tell it to monitor on the usb ethernet nic so it knows that its receiving monitored traffic from my HP switch port 25 mirrored traffic.