Segmentation is the foundation of any defence-in-depth strategy, but VLANs and rules drift as new services are added, devices are connected, and contractors plug in equipment. The OPNsense firewall sits at the centre of the segmentation model and a quarterly review confirms that what is documented is what is actually enforced.
When to use
Use this checklist once per quarter on every OPNsense firewall that segments multiple VLANs, before any major network refresh, and immediately after any incident where lateral movement is suspected. It also pairs with the monthly rule review: the segmentation review looks at intent and zone design; the rule review looks at implementation.
How to use
Pull the current segmentation map from the operator’s documentation and the OPNsense rule set per interface. Walk the list, mark each item, and follow up on every critical finding the same week. Capture the diff between this quarter and the previous quarter and file it with the change system.