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Running a OPNsense firewall in a VM? (slrpnk.net)
submitted 7 months ago by poVoq@slrpnk.net to c/selfhosted@lemmy.world
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I am not overly happy with my current firewall setup and looking into alternatives.

I previously was somewhat OK with OPNsense running on a small APU4, but I would like to upgrade from that and OPNsense feels like it is holding me back with it's convoluted web-ui and (for me at least) FreeBSD strangeness.

I tried setting up IPfire, but I can't get it to work reliably on hardware that runs OPNsense fine.

I thought about doing something custom but I don't really trust myself sufficiently to get the firewall stuff right on first try. Also for things like DHCP and port forwarding a nice easy web GUI is convenient.

So one idea came up to run a normal Linux distro on the firewall hardware and set up OPNsense in a VM on it. That way I guess I could keep a barebones OPNsense around for convenience, but be more flexible on how to use the hardware otherwise.

Am I assuming correctly that if I bind the VM to hardware network interfaces for WAN and LAN respectively it should behave and be similarly secure to a bare metal firewall?

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[–] ptz@dubvee.org 2 points 7 months ago* (last edited 7 months ago) (1 children)

Am I assuming correctly that if I bind the VM to hardware network interfaces for WAN and LAN respectively it should behave and be similarly secure to a bare metal firewall?

Correct.

I did that in my old playground VMware stack. I'll leave you with my cautionary tale (though depending on the complexity of your network, it may not fully apply).

My pfSense (OPNsense didn't exist yet) firewall was a VM on my ESX server. I also had it managing all of my VLANs and firewall rules and everything was connected to distributed vSwitches in vmware.. Everything worked great until I lost power longer than my UPS could hold on and had to shut down.

Shutdown was fine, but the cold start left me in a chicken/egg situation. vSphere couldn't connect to the hypervisors because the firewall wasn't routing to them. I could log into the ESX host directly to start the pfSense VM, but since vSphere wasn't running, the distributed switches weren't up.

The moral is: If you virtualize your core firewall, make sure none of the virtualization layers depend on it. πŸ˜†

[–] poVoq@slrpnk.net 3 points 7 months ago (1 children)

Thanks for the quick reply.

What about the LAN side: Can I bridge that adapter to the internal network of the VM host somehow to avoid an extra hop to the main switch and back via another network port?

[–] ptz@dubvee.org 3 points 7 months ago* (last edited 7 months ago)

May depend on your hypervisor, but generally yes. Should be able to give the VM a virtual NIC in addition to the two physical ones you bind, and it shouldn't care about the difference when you create a LAN bridge interface.

Depending on your setup/layout, either enable spanning tree or watch out for potential bridge loops, though.