VLAN & ACL Configuration: Implementing the 3-Zone Model

The 3-Zone Network Segmentation Model is the engineering standard for protecting a vessel’s Essential Services. By establishing firewalled boundaries between Operational Technology (OT), Corporate IT, and Untrusted guest networks, we ensure that a compromise in one zone cannot propagate to critical ship functions.

Step 1: Logical Isolation via VLAN Tagging

The first step is to logically segment the physical switch fabric into three distinct broadcast domains. This prevents “flat network” risks where a single infected device can see the entire vessel’s traffic.

Step 2: The Firewall as the “Conduit” Enforcer

In accordance with IEC 62443, traffic between zones must pass through a secure “Conduit.” In this model, the Firewall acts as that conduit. All Inter-VLAN routing must be disabled on the switches and offloaded to the firewall (Router-on-a-Stick or Multi-interface) to ensure 100% packet inspection.