The remaining server left to create in my lab is a Security Onion server. Security Onion is an out of the box blend of multiple open source tools that feed a central alert dashboard. I actually created a whole separate Pluralsight course called Security Onion Concepts and Basic Functionality if you are interested. The course covers the fundamentals, installation, and basic operation of the tool. This post is focused on capturing network traffic using my lab’s Security Onion server. To enable that, I configure a SPAN port for Security Onion in Proxmox on my pfsense virtual machine.
Configure physical NIC passthrough on the host
Prerequisite: Installing a Network Firewall Using Pfsense in Proxmox
My Proxmox lab has multiple hosts which significantly complicate this operation. The Security Onion server and pfsense firewall are located on separate hosts which means I have to pass the network traffic between hosts. I enabled this capability previously with software defined networking. There was a problem though, this does not support SPAN ports effectively. The best way I found to enable a SPAN port in Proxmox is to configure a physical NIC passthrough on the host. This allows me to assign a physical port on the host directly to a virtual machine which successfully passes all traffic.
The first step I took is to enable IOMMU in the /etc/default/grub file by adding the line below as seen in the image.
GRUB_CMDLINE_LINUX_DEFAULT="quiet intel_iommu=on"
Then I ran update-grub and reboot the machine. To check that the setting is correct after reboot, I ran the command below and looked for “IOMMU enabled”.
# dmesg | grep -e DMAR -e IOMMU
Next I added the required modules to enable physical NIC passthrough by editing the /etc/modules file and adding the modules in the image below.
Just to be safe, I rebooted the machine at this point and then checked that I could add a PCI device in the hardware setting in Proxmox.
Configure a SPAN port for Security Onion in Proxmox
Now that I can map a physical NIC to one of my virtual machines, I added one of the host ethernet adapters to the hardware on my pfsense virtual machine.
To make this work correctly on my old servers, I also had to enable unsafe interrupts with this command:
# echo "options vfio_iommu_type1 allow_unsafe_interrupts=1" > /etc/modprobe.d/iommu_unsafe_interrupts.conf 
Now when I access the pfsense interface menu from the command line, the new interface is available as bce0.
I assigned the interface the name OPT2 and then in the web configurator I enabled it and gave it a description of SPANport.
To configure a SPAN port in pfsense, you actually create a bridge within the interface menu. I went to Interfaces > Interface Assignments > Bridges and made a new one to create the SPAN port. I selected the LAN interface, added a description and then selected the SPANPORT interface under Span Port in the advanced configuration.
To complete my lab setup I did the same thing for the DMZ network, leaving me with two bridges.
The last step to verify operation is to test the SPAN port. To test, I used the packet capture tool in pfsense and set the interface to SPANPORT. I also enabled promiscuous mode to capture all data seen by the adapter.
Once I ran it, I could see multiple packets showing it was working as intended.
On the Security Onion server I will add another physical adapter, just like the pfsense machine. Then I will connect the interfaces directly with an ethernet cable.
Skipping ahead a bit to show it works
The output in Security Onion is not something I cover in the lab build, but it worked as configured in this post. Here is a tcpdump on my Security Onion Server and an overview of alerts.
I covered the how to install in a Pluralsight course, and you could also follow their documentation to build it. Security Onion is really one of the last steps to creating the basic structure of this lab other than adding the Kali machine and enabling remote access, but I also cover in the next post how to add VulnHub machines to the DMZ.
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