segmentation

A structured review of how a network is divided into separate security zones and how traffic moves between them. It uses Zero Trust, which requires verification instead of trusting devices merely because of their network location, and CIS security controls.

In plain words
What is it for?
Use it to review VLANs, firewalls, micro-segmentation, and DMZs, or to plan isolation for cloud migrations, compliance work, incidents, or merged networks.
Why use it?
It helps identify weak trust boundaries and limit how far an attacker can move through a network.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/unitoneai/securityskills/segmentation
Any agent
npx skills add UnitOneAI/SecuritySkills --skill segmentation
Clone the repo
git clone --depth 1 https://github.com/UnitOneAI/SecuritySkills

Made for: Claude Code, Codex.

Per session 78 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 4,105 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00078 $0.04105
Opus 5 $0.00039 $0.02053
Sonnet 5 $0.00016 $0.00821
Haiku 4.5 $0.00008 $0.00411

Measured 2d ago against content hash ce782885e86c, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

segmentation scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/network/segmentation/SKILL.md · 386 lines

How it starts

The opening of the file, as written. The whole thing — 386 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Network Segmentation Review

A structured, repeatable process for evaluating network segmentation architecture against NIST SP 800-207 (Zero Trust Architecture) and CIS Controls v8 Control 12 (Network Infrastructure Management). This skill produces a segmentation maturity assessment with zone mapping, trust boundary analysis, east-west traffic control evaluation, and prioritized remediation guidance.


When to Use

If a target is provided via arguments, focus the review on: $ARGUMENTS

  • Architecture reviews for new or modified network designs.
  • Zero Trust readiness assessments.
  • PCI DSS scoping exercises requiring CDE segmentation validation (PCI DSS v4.0 Requirement 1.3).
  • Post-incident reviews where lateral movement was observed or suspected.
  • Cloud migration planning requiring workload isolation design.
  • Merger/acquisition network integration planning.

Context

Network segmentation is the foundational control that limits blast radius. NIST SP 800-207 Section 2 defines Zero Trust Architecture as requiring "no implicit trust granted to assets or user accounts based solely on their physical or network location." CIS Controls v8 Control 12 requires enterprises to "establish, implement, and actively manage network devices, in order to prevent attackers from exploiting vulnerable network services and access points." Effective segmentation moves beyond flat VLANs to enforce policy at the workload level, restricting east-west traffic between systems that have no legitimate communication requirement.


Process

Step 1: Discovery -- Locate Network Architecture Artifacts

Use Glob and Grep to locate network configuration files, diagrams-as-code, and infrastructure definitions.

Patterns to search:

# Infrastructure-as-Code
**/*.tf                  # Terraform (VPCs, subnets, route tables, security groups)
**/vpc*
**/subnet*
**/network*

# Kubernetes network policies
**/NetworkPolicy*
**/network-policy*
**/calico*
**/cilium*

# Cloud-native
**/firewall-rule*
**/security-group*
**/nsg*
**/route-table*

# Traditional
**/vlan*
**/*.acl
**/interfaces*

Read the full file on GitHub · 386 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 386 lines · 78 tokens per session scan A ce782885e86c

Subscribe to this mod's changes

segmentation is a skill published in the GitHub repository UnitOneAI/SecuritySkills (58 stars, last pushed 2mo ago), licensed MIT. It adds 78 tokens to every session and 4,105 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.