implementing-network-segmentation-for-ot

# Implementing Network Segmentation for OT ## When to Use - When an OT security assessment reveals a flat network with no segmentation between Purdue levels - When implementing IEC 62443 zone/conduit architecture after completing risk assessment (IEC 62443-3-2) - When separating IT and OT networks as part of an IT/OT convergence security initiative - When deploying a DMZ between corporate IT and OT to protect industrial systems from IT-originating threats - When segmenting safety instrumented systems (SIS) from basic process control systems (BPCS) **Do not use** for IT-only microsegmentation without OT components (see implementing-zero-trust-in-cloud), or for initial zone design without prior traffic analysis (see performing-ot-network-security-assessment first). ## Prerequisites - Complete traffic baseline from passive monitoring (minimum 2-4 weeks of capture data) - Asset inventory with Purdue level classifications for all OT devices - Industrial-grade network switches with VLAN support and port security - OT-aware firewalls (Cisco ISA-3000, Fortinet FortiGate Rugged, Palo Alto with OT Security) - Maintenance window schedule for network changes - Rollback plan approved by operations management ## Workflow ### Step 1: Design Segmentation Architecture Based on Traffic Baseline Use the traffic baseline to design VLAN and firewall architecture that preserves all legitimate communication paths while isolating zones. ```python #!/usr/bin/env python3 """OT Network Segment...