Network Segmentation Best Practices

Network segmentation divides your network into separate zones with controlled access between them. This limits the "blast radius" of security breaches and protects sensitive systems from office-based threats. For manufacturing operations, proper segmentation is both a security best practice and often a compliance requirement.

Why Network Segmentation Matters

Contain Security Breaches

When a user clicks a phishing link and gets malware on their workstation, segmentation prevents that malware from spreading to:

• Production control systems
• CAD/CAM workstations with engineering data
• Servers containing customer information
• Quality management systems with certification records

Without segmentation, one infected laptop can compromise your entire operation.

Meet Compliance Requirements

Many regulations require or strongly recommend network segmentation:

• CMMC Level 2: Requires logical separation of CUI from other data
• NIST 800-171: System and communications protection controls
• ITAR: Controlled environment for defense articles and technical data
• PCI DSS: Cardholder data must be on separate network segment

Improve Network Performance

Segmentation reduces broadcast traffic and network congestion. Production systems get dedicated bandwidth without competing with office internet usage.

Simplify Security Management

Different network zones can have different security policies. Production systems can have stricter controls than general office workstations.

Common Network Segments for Manufacturing

1. General Office Network

Purpose: Standard business workstations and applications

Devices:

• Employee workstations
• Printers and copiers
• Conference room displays
• Office phones (VoIP)

Access: Internet access allowed, can access approved servers

Security level: Standard corporate policies

2. Production/Shop Floor Network

Purpose: Manufacturing equipment and control systems

Devices:

• CNC machines and controllers
• PLCs (Programmable Logic Controllers)
• SCADA systems
• Inspection equipment
• Inventory scanners

Access: No internet access, limited access to office network

Security level: High—these systems often can't run antivirus or receive updates easily

3. Engineering/CAD Workstation Network

Purpose: Design and engineering systems with sensitive intellectual property

Devices:

• CAD/CAM workstations
• Engineering file servers
• 3D printers and prototyping equipment
• Simulation and analysis systems

Access: Controlled internet access, encrypted connections to partners

Security level: Very high—protect designs and technical data

4. Server/Data Center Network

Purpose: Backend systems and databases

Devices:

• File servers
• Database servers
• ERP systems
• Email servers (if on-premises)
• Backup systems

Access: No direct internet access, strict firewall rules

Security level: Very high—contains all company data

5. ITAR/CUI Enclave (Defense Contractors)

Purpose: Isolated environment for controlled unclassified information

Devices:

• Workstations accessing ITAR data
• Servers storing CUI
• Systems used for defense contracts

Access: Heavily restricted, no internet, strict access controls

Security level: Maximum—CMMC Level 2+ requirements

6. Guest WiFi Network

Purpose: Visitor internet access

Devices: Visitor smartphones, laptops, tablets

Access: Internet only, no access to any business resources

Security level: Isolated—assume compromised

7. Management/Admin Network

Purpose: Infrastructure management

Devices:

• Network switches and routers
• Firewalls and security appliances
• Server management interfaces (iDRAC, iLO)

Access: IT admin access only, no general user access

Security level: Critical—compromise here means full network compromise

Implementation Approaches

Physical Segmentation

Method: Separate physical network infrastructure for each segment

Pros: Maximum security, complete isolation

Cons: Expensive, requires duplicate equipment, difficult to manage

Best for: Small networks or extremely sensitive environments

VLAN Segmentation (Most Common)

Method: Virtual LANs on managed switches with firewall between VLANs

Pros: Cost-effective, flexible, industry standard

Cons: Requires proper firewall configuration, possible VLAN hopping attacks if misconfigured

Best for: Most small to mid-sized businesses

Software-Defined Networking (SDN)

Method: Micro-segmentation using software-defined rules

Pros: Highly granular control, dynamic policies

Cons: Complex to implement, expensive

Best for: Larger organizations or those with advanced security requirements

Firewall Rules Between Segments

Segmentation only works if you control traffic between zones. Use a "default deny" approach:

Example Firewall Rules:

Office Network → Production Network:

• Allow: Specific authorized users to specific systems (for programming CNC machines)
• Allow: Inventory system queries to production database
• Deny: Everything else

Production Network → Internet:

• Deny: All outbound connections (production systems shouldn't need internet)

Engineering Network → File Server:

• Allow: CAD file storage access
• Allow: Version control system
• Log: All file transfers

Guest WiFi → Everywhere:

• Allow: Internet only
• Deny: All internal resources

Implementation Best Practices

Start with Documentation

• Map your current network
• Identify all devices and their functions
• Determine sensitivity/criticality of each system
• Document data flows (what needs to talk to what)

Design Before Implementation

• Create network diagram showing all segments
• Define firewall rules for each segment boundary
• Plan IP addressing scheme (different subnets for each VLAN)
• Identify required access between zones

Implement Gradually

• Phase 1: Separate guest WiFi
• Phase 2: Isolate production/shop floor
• Phase 3: Create engineering enclave
• Phase 4: Implement CUI/ITAR enclave if needed

Test Thoroughly

• Verify authorized communications work
• Confirm unauthorized communications are blocked
• Test from multiple source segments
• Document all testing results

Monitor and Maintain

• Enable logging on firewalls and switches
• Review denied traffic (may indicate needed rules or attack attempts)
• Update firewall rules as needs change
• Conduct annual network security assessments

Common Mistakes to Avoid

1. Segmenting but not enforcing with firewalls
VLANs alone don't provide security. You need firewall rules between segments.

2. Too permissive firewall rules
"Allow all from Office to Production" defeats the purpose. Be specific about what's allowed.

3. Not updating rules as needs change
Document changes and review rules quarterly.

4. Forgetting about WiFi
WiFi can bridge segments if not properly configured. Use separate SSIDs for different zones.

5. Poor documentation
If you can't explain why a rule exists, you probably need to revisit your segmentation design.

6. Assuming internal traffic is safe
Once attackers are inside, flat networks let them move freely. Segmentation forces them through chokepoints where you can detect them.

Cost Considerations

Implementing segmentation requires investment in:

• Managed switches: VLAN-capable, typically $200-2,000 per switch depending on port count
• Firewall: $1,000-10,000+ depending on throughput and features needed
• Professional services: Design and implementation, $5,000-25,000
• Ongoing management: Monitoring and rule updates

While not free, segmentation is far less expensive than recovering from a major breach or losing defense contracts due to lack of compliance.

The Bottom Line

Network segmentation is fundamental to modern cybersecurity. It protects production systems from office threats, contains breaches, and enables compliance with regulations like CMMC. For manufacturing and aerospace companies, proper segmentation isn't optional—it's essential for protecting operations and maintaining competitive advantage.

Start with a clear design, implement gradually, and maintain proper firewall rules between segments. The investment pays dividends in security, compliance, and operational resilience.