Why Network Security Is Non-Negotiable for ISO 27001 and NIS2 Compliance

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Network security is the backbone of ISO 27001 and NIS2 compliance. Organisations that master network defence not only meet regulatory demands but also reduce risk, protect sensitive data, and ensure operational continuity in the face of evolving threats.

What’s at stake

Modern organisations face a relentless barrage of cybersecurity threats targeting their networks. From ransomware and data breaches to supply chain attacks, the consequences of inadequate network security are severe: financial loss, regulatory penalties, reputational damage, and operational disruption. ISO/IEC 27001:2022 and NIS2 both demand proactive network protection, making this a board-level concern for any entity handling sensitive data or critical services.

The risks extend beyond IT. Network failures can halt production, disrupt customer-facing services, and expose personal or regulated data. NIS2, in particular, raises the stakes for essential and important entities—such as healthcare, energy, and digital infrastructure providers—by imposing strict requirements for risk management, incident response, and continuity. Under both standards, the expectation is clear: networks must be resilient, segmented, and continuously monitored to prevent, detect, and recover from incidents.

Consider a mid-sized manufacturer with a segmented network supporting both production and administrative functions. A misconfigured firewall exposes the production network, leading to a ransomware attack that halts operations for days. Not only does this result in lost revenue, but it triggers regulatory scrutiny and damages customer trust. The incident highlights how network security failures can quickly escalate from technical glitches to business crises.

Network security is not just about technology—it’s about ensuring the ongoing confidentiality, integrity, and availability of all systems and data. Regulatory pressure is mounting: NIS2 mandates proportionate risk management measures, and ISO/IEC 27001:2022 embeds network controls into its core ISMS framework. Failure to comply can mean hefty fines, legal action, and lasting reputational harm.

What good looks like

Organisations that excel in network security achieve more than regulatory compliance; they create an environment where risks are managed, incidents are swiftly contained, and business objectives are safeguarded. Good practice is rooted in the principles and control themes of ISO/IEC 27001:2022 and NIS2.

Effective network security begins with robust perimeter defences, segmentation of critical assets, and continuous monitoring. ISO/IEC 27001:2022’s Annex A controls—especially those mapped to NIS2—demand technical and organisational measures that adapt to risk exposure and operational needs. This means deploying firewalls, intrusion detection/prevention systems (IDS/IPS), and secure routing, but also formalising policies and procedures for incident response, access management, and supplier oversight.

A compliant organisation will have documented and operationalised network security policies, approved by top management and acknowledged by staff and third parties. Networks are architected to prevent lateral movement of threats, with sensitive zones isolated and access tightly controlled. Monitoring and logging are active, enabling rapid detection and forensic analysis. Regular risk assessments inform the design and operation of network controls, ensuring they remain fit for purpose as threats evolve.

For example, a healthcare provider subject to NIS2 segments its patient data network from general IT services, applies strict access controls, and monitors for unusual activity. When a suspected breach occurs, the incident response team isolates affected segments, analyses logs, and restores operations—demonstrating resilience and regulatory alignment.

Good network security is measurable. It’s evidenced by audit trails, policy acknowledgements, and a track record of incident containment. Controls are mapped to both ISO/IEC 27001:2022 and NIS2 requirements, with cross-references ensuring nothing falls through the cracks.¹ Zenith Blueprint

Practical path

Achieving effective network security for ISO 27001 and NIS2 is a journey that blends technical controls, documented policies, and operational discipline. Success hinges on clarity of scope, proportionality of measures, and demonstrable evidence. The following steps, grounded in ClarySec artefacts, provide a pragmatic roadmap.

Start by defining the scope of network security—covering all components, from wired and wireless infrastructure to routers, switches, firewalls, gateways, and information systems. Documented policies, such as the Network Security Policy, establish the rules for secure design, usage, and management, ensuring everyone understands their responsibilities.² Network Security Policy

Next, implement technical controls that align with ISO/IEC 27001:2022 and NIS2. This means deploying segmentation models, firewall rulesets, and exception processes for sensitive systems. Continuous monitoring is essential, with logging and alerting for suspicious behaviour. Regular risk assessments and vulnerability scans identify emerging threats, informing updates to controls and procedures.

Operationalise access control policies to restrict entry to critical network zones. Ensure that privileged accounts and system administration credentials are managed according to best practice, with periodic reviews and prompt offboarding. Supplier relationships must be governed by security clauses and oversight, especially when relying on external network infrastructure.³ Zenith Controls

Embed incident response and business continuity measures into network operations. Document procedures for detecting, responding to, and recovering from network incidents. Test these processes regularly, simulating scenarios such as ransomware outbreaks or supply chain disruptions. Maintain evidence of policy acknowledgement and training, ensuring staff and third parties are aware of expectations.

A real-world example: An SME in the financial sector uses the Zenith Blueprint to map ISO 27001 controls to NIS2 articles, deploying segmented networks, firewalls, and IDS. When a supplier’s VPN credentials are compromised, rapid detection and isolation prevent wider impact, and documented evidence supports regulatory reporting.

The practical path is iterative. Each improvement cycle draws on lessons learned and audit findings, strengthening both compliance and resilience.

Policies that make it stick

Policies are the backbone of sustainable network security. They provide clarity, accountability, and enforceability—ensuring that technical controls are supported by organisational discipline. For ISO 27001 and NIS2, documented policies are not optional; they are required evidence of compliance.

The Network Security Policy is central. It defines requirements for protecting internal and external networks from unauthorised access, service disruption, data interception, and misuse. It covers secure design, usage, and management, and mandates segmentation, monitoring, and incident handling. Approval by top management and acknowledgement by staff and third parties are critical for demonstrating a culture of security.⁴ Network Security Policy

Other supporting policies include the Access Control Policy, Privileged Accounts Management Policy, and Supplier Relationship Policy. Together, these ensure that network access is restricted, high-risk accounts are tightly managed, and external dependencies are governed with security in mind.

For instance, a logistics company introduces a formal Network Security Policy and requires all staff and contractors to sign an acknowledgement. This step not only satisfies NIS2 and ISO 27001 requirements but also sets expectations for behaviour and accountability. When a network incident occurs, the documented policy enables a swift, coordinated response.

Policies must be living documents—reviewed, updated, and communicated as threats and technologies evolve. Evidence of policy updates, staff training, and incident response exercises demonstrate ongoing compliance and maturity.

Checklists

Checklists translate policy and strategy into action. They help organisations build, operate, and verify network security in a structured, repeatable way. For ISO 27001 and NIS2 compliance, checklists provide tangible evidence of control implementation and ongoing assurance.

Build: Network Security for ISO 27001 and NIS2

Building network security starts with a clear understanding of requirements and risks. The checklist ensures foundational controls are in place before operations begin.

• Define scope: List all network components, including wired/wireless infrastructure, routers, switches, firewalls, gateways, and cloud services.
• Approve and communicate the Network Security Policy to all relevant personnel and third parties.⁵
• Architect network segmentation, isolating critical assets and sensitive data zones.
• Deploy perimeter defences: firewalls, IDS/IPS, VPNs, and secure routing.
• Establish access control mechanisms for network entry points and privileged accounts.
• Document supplier relationships, embedding security clauses in contracts.
• Map controls to ISO 27001:2022 Annex A and NIS2 articles using the Zenith Blueprint.¹

A regional retailer, for example, uses this checklist to build a segmented network for payment systems, ensuring PCI DSS, ISO 27001, and NIS2 controls are aligned from day one.

Operate: Ongoing Network Security Management

Operating secure networks requires vigilance, periodic review, and continuous improvement. This checklist focuses on day-to-day activities that maintain compliance and resilience.

• Monitor networks continuously for anomalies, using SIEM and log management solutions.
• Conduct regular vulnerability assessments and penetration tests.
• Review and update firewall rulesets, segmentation models, and exception processes.
• Manage privileged accounts, with periodic access reviews and immediate offboarding upon role changes.
• Train staff and third parties on security policies and incident response procedures.
• Maintain evidence of policy acknowledgement and training.
• Conduct supplier security reviews and audits.

An SME in healthcare, for instance, operates its network with continuous monitoring and quarterly access reviews, catching and resolving misconfigurations before they escalate.

Verify: Audit and Assurance for Network Security

Verification closes the loop, providing assurance that controls are effective and compliance is sustained. This checklist supports internal and external audits.

• Collect evidence of policy approval, communication, and acknowledgement.
• Document risk assessments, vulnerability scans, and incident response exercises.
• Maintain audit trails for network changes, access reviews, and supplier oversight.
• Map audit findings to ISO 27001:2022 and NIS2 requirements using the Zenith Controls library.³
• Address gaps and implement corrective actions, updating policies and controls as needed.
• Prepare for regulatory inspections and customer audits, with evidence ready for review.

A financial services firm, anticipating a regulator audit, uses this checklist to organise documentation and demonstrate compliance across network security domains.

Common pitfalls

Despite best intentions, organisations frequently stumble on network security for ISO 27001 and NIS2. These pitfalls are blunt, costly, and often preventable.

One major pitfall is treating network security as a “set and forget” exercise. Controls may be deployed, but without regular review and testing, gaps emerge—outdated firewall rules, unmonitored privileged accounts, and unpatched vulnerabilities. Compliance becomes a paper exercise, not a living practice.

Another pitfall is failing to segment networks properly. Flat networks allow threats to move laterally, amplifying the impact of breaches. NIS2 and ISO 27001 both expect logical and physical separation of critical assets, yet many organisations overlook this in favour of convenience.

Supplier risk is another weak point. Relying on third-party network services without robust security clauses, oversight, or audits exposes organisations to cascading failures and regulatory exposure. Incidents at suppliers can quickly become your problem, especially under NIS2’s supply chain requirements.

Policy acknowledgement is often neglected. Staff and contractors may be unaware of expectations, leading to risky behaviour and poor incident response. Documented evidence of policy communication and training is vital.

For example, a tech startup outsources network management but fails to audit its provider. When the provider suffers a breach, customer data is exposed, triggering regulatory action and damaging the startup’s reputation.

Avoiding these pitfalls requires discipline: regular reviews, strong segmentation, supplier governance, and clear policy communication.

Next steps

• Explore the Zenith Suite for integrated network security controls and compliance mapping: Zenith Suite
• Assess your readiness with the Complete SME & Enterprise Combo Pack, including policy templates and audit tools: Complete SME + Enterprise Combo Pack
• Fast-track your network security journey with the Full SME Pack, tailored for rapid ISO 27001 and NIS2 alignment: Full SME Pack

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