Implementing Purdue Model Network Segmentation

---
name: implementing-purdue-model-network-segmentation
description: Use when implement network segmentation based on the Purdue Enterprise
  Reference Architecture (PERA) model to separate industrial control system networks
  into hierarchical security zones from Level 0 physical process through Level 5 enterprise,
  enforcing strict traffic control between OT and IT domains. . Use when working with
  implementing purdue model network segmentation.
domain: cybersecurity
tags:
- ot-security
- ics
- purdue-model
- network-segmentation
- iec62443
- defense-in-depth
- dmz
- scada
subdomain: ot-ics-security
version: '1.0'
author: oyi77
license: Apache-2.0
nist_csf:
- PR.IR-01
- DE.CM-01
- ID.AM-05
- GV.OC-02
category: cybersecurity
---

# Implementing Purdue Model Network Segmentation

## Overview

Cybersecurity skill for implementing purdue model network segmentation. Follows industry best practices and security standards.

## When to Use
**Trigger phrases:**
- "implementing purdue model network segmentation"
- "Implement network segmentation based on the Purdue Enterprise Reference Architec"


- When designing or retrofitting network architecture for an ICS/SCADA environment
- When implementing IEC 62443 zone and conduit requirements in a brownfield plant
- When creating the IT/OT DMZ (Level 3.5) to control data flow between enterprise and control networks
- When remediating audit findings about flat OT networks or direct IT-to-OT connectivity
- When segmenting a converged IT/OT network after an acquisition or merger

**Do not use** for micro-segmentation within a single Purdue level (see implementing-zone-conduit-model-for-ics), for cloud-native environments without traditional ICS networks, or for network segmentation in purely IT environments.


## When NOT to Use

- When you lack proper authorization for testing
- For production systems without change management
- When the task requires legal or compliance expertise beyond technical scope


## Prerequisites

- Complete OT asset inventory with Purdue level classification for each device
- Network architecture diagram showing current topology, VLANs, and firewall placements
- Industrial firewalls capable of deep packet inspection for OT protocols (Palo Alto, Fortinet, Cisco)
- Understanding of required data flows between Purdue levels (historian replication, remote access, patch distribution)
- Change management approval from plant operations for network modifications

## Workflow

```python
# Example: IOC detection
import re

IOC_PATTERNS = {
    "ip": r"\b(?:\d{1,3}\.){3}\d{1,3}\b",
    "domain": r"\b[a-z0-9-]+\.[a-z]{2,}\b",
    "hash_md5": r"\b[a-f0-9]{32}\b",
    "hash_sha256": r"\b[a-f0-9]{64}\b",
}

def extract_iocs(text: str) -> dict:
    return {k: re.findall(v, text) for k, v in IOC_PATTERNS.items()}
```

1. **Assess Requirements** — Evaluate current environment and define purdue model network segmentation implementation requirements.
2. **Design Architecture** — Plan the purdue model network segmentation architecture, including components, integrations, and data flows.
3. **Configure Components** — Set up and configure each purdue model network segmentation component according to best practices.
4. **Test Integration** — Validate that all components work together. Run functional and security tests.
5. **Deploy to Production** — Roll out the implementation with monitoring and rollback capabilities.
6. **Validate and Document** — Verify the implementation meets requirements. Document configuration and runbooks.

## Tools

- **Configuration Management** — Infrastructure as code and automation
- **Monitoring Stack** — Observability and alerting
- **Documentation Platform** — Runbooks and architecture docs


## Process

1. **Prepare** — Gather requirements, verify prerequisites, set up environment
1. **Execute** — Run implementing purdue model network segmentation workflow with configured parameters
1. **Verify** — Validate output meets requirements, document results

## Verification

- [ ] All purdue model network segmentation procedures executed completely and documented
- [ ] Findings validated against multiple data sources
- [ ] False positives identified and filtered
- [ ] Results documented with evidence and timestamps
- [ ] Recommendations provided with risk-based prioritization

## Anti-Rationalization Table

| Rationalization | Reality |
|---|---|
| "We are too small to be targeted" | Automated attacks target everyone. Size does not matter. |
| "Security slows us down" | A breach slows you down 100x more. Build security in from the start. |
| "We will fix it after launch" | Vulnerabilities in production are exploited within hours. Fix before deploy. |