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 Segmentation Design Tool.

Analyzes traffic baseline data and generates a segmentation design
with VLAN assignments, firewall rules, and migration plan.
"""

import json
import sys
from collections import defaultdict
from dataclasses import dataclass, field, asdict
from ipaddress import ip_address, ip_network


@dataclass
class VLANDesign:
    vlan_id: int
    name: str
    purdue_level: str
    subnet: str
    gateway: str
    description: str