Alright team, buckle up. We just completed a forklift migration from a pair of ancient Cisco ASA 5510s (running code so old it felt like digital archaeology) to a HA pair of pfSense firewalls. This was for a mid-sized manufacturing client with about 300 users and a handful of critical on-premise servers. The goal was modern security, VPN stability, and finally getting some usable reporting.
I've seen these migrations go sideways, leaving everyone in a panic. This one, thankfully, was a relative success. Here's what we did right that made the difference:
**We treated the ASA config as a legacy artifact, not a blueprint.**
Our first move was to export the ASA config and then... largely ignore it for the initial design. We mapped the actual business requirements from scratch with the client's IT lead.
* What services truly need to be exposed?
* Who needs what kind of VPN access (we standardized on IKEv2/IPsec for road warriors and OpenVPN for a small vendor group)?
* What are the real internal traffic flows? We found a dozen old NAT statements and ACLs pointing to decommissioned servers. The old config was a history book of "temporary" fixes from 2012. Starting fresh prevented us from blindly porting over a decade of cruft.
**We built a mirrored lab environment that actually mirrored.**
This wasn't just a spare box. We virtualized pfSense, replicated their WAN handoff (using a spare public IP block from their ISP for testing), and created a mini-version of their internal VLAN structure. We then painstakingly recreated their key policies and did failover testing for days. The cost in time upfront was significant, but it meant our migration window was a known quantity. When we cut over, we already knew exactly how the HA failover would behave and had our monitoring thresholds set.
**We invested deeply in change management for the network team.**
The two network admins were ASA CLI wizards but had zero pfSense experience. Our "knowledge transfer" wasn't a 1-hour handoff. We did three workshops:
* One on the philosophy of the GUI and where to find the equivalents of their ASA commands.
* A deep dive on the new reporting packages (ntopng, Darkstat) and how they were superior to the ASDM graphs they hated.
* A "break-glass" session where we simulated failures and showed them how to troubleshoot in the new environment.
This turned them from apprehensive stakeholders into active champions. They even started optimizing rules during the testing phase.
**We phased the migration by risk, not by convenience.**
We didn't do a "big bang" cutover. The sequence was:
1. Deployed the pfSense boxes in parallel, handling only outbound internet and guest Wi-Fi for a week. Low risk, high visibility for users.
2. Migrated the site-to-site VPNs over a weekend. This was the biggest worry, but the lab work paid off.
3. Finally, moved the inbound NAT rules for email and their ERP system in a separate, planned maintenance window.
Each step gave us a rollback point and built confidence. The final cutover for the core servers felt like a non-event.
The result? Performance is up, the client has dashboards they actually look at, and the VPN help desk tickets have dropped by about 80%. The key was respecting the scale of the change—it's not just a hardware swap, it's a cultural and operational shift for the team managing it. The scars from past projects taught us that skipping any of these steps is asking for a long, painful night.
Implementation is 80% process, 20% tool.
That makes so much sense. I've been trying to learn Terraform for managing AWS security groups and the hardest part is untangling why an old rule exists before I can even think about rewriting it in code.
> largely ignore it for the initial design
I never thought of that. I always assumed the old config was the single source of truth you had to decipher. Starting from the actual business needs seems way less painful. Did you use any tools to map those real internal flows, or was it mostly just talking to people and checking logs?