Migration to Opensense from Pfsense: can I set it up offline?

[patrick3000]

I need to migrate my router/firewall to new hardware as an upgrade to accommodate faster speeds on certain subnets (10 and 2.5 gbps). Currently, I'm using Pfsense and have done so for many years. However, I'm considering installing Opensense on the new hardware because Pfsense CE isn't being updated very often and Netgate clearly no longer has a commitment to open source.

Does anyone know if I can set up Opensense on the new hardware (mostly) offline? Like either directly attached to my laptop or else on my existing network through a switch with only one interface attached? The reason is that my setup is moderately complex, and I can't afford any significant downtime, especially since my spouse relies on the network to work from home. The longest I could afford to take it down for is a couple of hours in the middle of the night.

I have two WANS, with fail-over in case one goes down, and three LAN subnets. Also, there is a lot of customization with firewall rules and aliases, NAT, the DNS resolver, and other things. Fortunately not a lot of add-ons. I used to run PF Blocker, but it caused too many problems and I uninstalled it last year.

So, what I'd like to do is leave PfSense running on the old hardware while I install Opensense on the new hardware, configure all the interfaces in Opensense while they're not actually attached to anything, set up all the firewall rules and aliases, etc. Then, when everything is ready, hook up the new hardware running Opensense to the network and decommission the old hardware.

Does anyone know if this will work? I'm concerned that maybe Opsense won't work or will give error messages if I try to set it up while the interfaces aren't attached to anything and are in a "down" state.

[TheAutomationGuy]

Just curious what your experience was with this?  I find myself in a similar situation.  I'm currently running pfSense, but have purchases another device that I want to set OPNsense up on.  I'll run it behind the pfSense firewall as I begin to explore it, but I'd love to hear your experiences in moving everything over eventually.

[Greelan]

It will work fine. This is exactly how I originally configured OPNsense. Connected it to a laptop, gave it a manual local IP and then spent a couple of days configuring as needed. Then deployed

You will need to turn off "block local IPs" on the wan interface initially while configuring (since wan will have a local IP) and then turn it back on when deployed