<!-- Copyright (c) 2026 defconxt. All rights reserved. -->
<!-- Licensed under AGPL-3.0 — see LICENSE file for details. -->
---
name: automating-network-segmentation-validation
description: >-
  Automate continuous validation of network segmentation controls by testing
  connectivity between zones, verifying firewall rules, detecting policy
  drift, and generating compliance evidence for PCI-DSS and zero trust.
domain: cybersecurity
subdomain: security-operations-automation
tags:
  - network-segmentation
  - firewall
  - validation
  - pci-dss
  - zero-trust
  - automation
version: "1.0"
author: defconxt
license: AGPL-3.0
metadata:
  mitre-attack: ["T1021"]
---

# Automating Network Segmentation Validation

## Overview

Network segmentation is a critical control but often degrades over time
through rule creep, emergency changes, and misconfigurations. This technique
automates validation by defining expected connectivity matrices, testing
actual reachability between zones, comparing against firewall policies, and
generating compliance evidence for PCI-DSS Requirement 1 and zero trust
architectures.

Mode: `[MODE: BLUE]` — Continuous segmentation assurance.

## Prerequisites

| Requirement | Details |
|---|---|
| Python 3.10+ with `requests`, `ipaddress` | Required |
| Network scanner access for reachability testing | Required |
| Firewall API access (Palo Alto, Fortinet, or iptables) | Required |
| Defined network zone inventory with expected policies | Required |

## Key Concepts

### Segmentation Policy Matrix

```python
from dataclasses import dataclass, field
from typing import Any


@dataclass
class SegmentationRule:
    """Expected connectivity rule between network zones."""

    src_zone: str
    dst_zone: str
    allowed_ports: list[int] = field(default_factory=list)
    protocol: str = "tcp"
    expected: str = "deny"  # "allow" or "deny"


POLICY_MATRIX: list[SegmentationRule] = [
    SegmentationRule("user", "production", [443], "tcp", "allow"),
    SegmentationRule("user", "database", [], "tcp", "deny"),
    SegmentationRule("production", "database", [5432, 3306], "tcp", "allow"),
    SegmentationRule("guest", "production", [], "tcp", "deny"),
    SegmentationRule("guest", "user", [], "tcp", "deny"),
    SegmentationRule("dmz", "internal", [], "tcp", "deny"),
]
```

### Reachability Testing

```python
import socket


def test_reachability(
    src_host: str,
    dst_host: str,
    port: int,
    timeout: int = 5,
) -> dict[str, Any]:
    """Test TCP reachability between two hosts."""
    try:
        sock = socket.create_connection((dst_host, port), timeout=timeout)
        sock.close()
        return {"src": src_host, "dst": dst_host, "port": port, "reachable": True}
    except (OSError, TimeoutError):
        return {"src": src_host, "dst": dst_host, "port": port, "reachable": False}
```

### Violation Detection

```python
def validate_segmentation(
    policy: list[SegmentationRule],
    test_results: list[dict[str, Any]],
) -> list[dict[str, Any]]:
    """Compare test results against expected segmentation policy."""
    violations: list[dict[str, Any]] = []
    for rule in policy:
        matching_tests = [
            t for t in test_results
            if t.get("src_zone") == rule.src_zone
            and t.get("dst_zone") == rule.dst_zone
        ]
        for test in matching_tests:
            if rule.expected == "deny" and test.get("reachable"):
                violations.append({
                    "type": "unauthorized_access",
                    "severity": "high",
                    "src_zone": rule.src_zone,
                    "dst_zone": rule.dst_zone,
                    "port": test.get("port"),
                    "expected": "deny",
                    "actual": "allow",
                })
            elif rule.expected == "allow" and not test.get("reachable"):
                violations.append({
                    "type": "broken_connectivity",
                    "severity": "medium",
                    "src_zone": rule.src_zone,
                    "dst_zone": rule.dst_zone,
                    "port": test.get("port"),
                    "expected": "allow",
                    "actual": "deny",
                })
    return violations
```

## Workflow

### Step 1: Define Segmentation Policy

```bash
node scripts/agent.js --action show-policy
```

### Step 2: Run Validation Tests

```bash
node scripts/agent.js --action validate
```

### Step 3: Generate Compliance Report

```bash
node scripts/agent.js --action compliance-report --framework pci-dss
```

## Detection

```yaml
title: Automating Network Segmentation Validation Detection
id: 53a7e9d4-dfc8-45a5-97c7-e1602496e6fb
status: experimental
description: Detects suspicious activity related to automating network segmentation validation techniques in security operations automation context
logsource:
  category: process_creation
  product: linux
detection:
  selection:
    CommandLine: "*automating*network*"
  condition: selection
level: medium
tags:
  - attack.t1021
  - attack.discovery
falsepositives:
  - Orchestration platform executing approved automation workflows
```


**Detection Opportunities**

| Indicator | Source | Detection Logic |
|---|---|---|
| Automating Network Segmentation Validation Detection | linux/process_creation | Sigma rule (medium) |
| ATT&CK Coverage | MITRE ATT&CK | T1021 |

## Verification

- [ ] All zone pairs tested against expected policy
- [ ] Unauthorized access paths flagged as violations
- [ ] Broken legitimate connectivity detected
- [ ] Compliance evidence generated with test timestamps

## References

- [PCI-DSS Requirement 1 — Network Segmentation](https://www.pcisecuritystandards.org/)
- [NIST SP 800-125B — Secure Virtual Network Configuration](https://csrc.nist.gov/publications/detail/sp/800-125b/final)
- [CIS Control 12 — Network Infrastructure Management](https://www.cisecurity.org/controls)
