ISO 27001 Annex A 8.21 is a security control that requires organizations to manage the security of services provided by networks, both internal and external. It mandates the identification and monitoring of service levels and security requirements (e.g., encryption, availability) within agreements to ensure that network services, such as ISPs or cloud connectivity, meet business needs and protect data integrity and confidentiality.
In this guide, I will show you exactly how to implement ISO 27001 Annex A 8.21 and ensure you pass your audit. You will get a complete walkthrough of the control, practical implementation examples, and access to the ISO 27001 templates and toolkit that make compliance easy.
I am Stuart Barker, an ISO 27001 Lead Auditor with over 30 years of experience conducting hundreds of audits. I will cut through the jargon to show you exactly what changed in the 2022 update and provide you with plain-English advice to get you certified.
Key Takeaways: ISO 27001 Annex A 8.21 Security of Network Services
ISO 27001 Annex A 8.21 requires organizations to identify and implement security requirements for all network services they use. This isn’t just about owning a router; it’s about managing your relationships with providers (ISPs, VPN vendors, Cloud Networking) to ensure they meet your security standards and maintain the uptime your business needs.
Core requirements for compliance include:
- Identify Service Requirements: You must define what you need from your network providers (e.g., “The ISP must provide 99.9% uptime,” or “The VPN must use AES-256 encryption”).
- Service Level Agreements (SLAs): Security and availability requirements should be written into your contracts. You cannot just “hope” the internet stays up; you need an agreement that defines what happens if it goes down.
- Monitoring & Review: It is not enough to sign a contract. You must monitor your service providers to ensure they are meeting their promises. This could include reviewing monthly uptime reports or checking their SOC 2 or ISO 27001 audit reports.
- Encryption & Data Separation: If you use a shared network service (like an MPLS or a Public Cloud), you must ensure your traffic is logically separated and encrypted so other customers of that provider cannot see your data.
Audit Focus: Auditors will look for External Validation:
- The Contract: “Show me the security clauses in your ISP or Managed Service Provider (MSP) agreement.”
- Uptime Proof: “Show me the report that proves your network provider met their 99.9% availability target last month.”
- Third-Party Assurance: “How do you know your provider is secure? Show me their latest ISO 27001 certificate or audit summary.”
What to Check in a Network Service Contract:
| Requirement | Why it matters | What to look for |
|---|---|---|
| Availability | Prevents business downtime. | Uptime guarantees (e.g., 99.9%). |
| Encryption | Protects data in transit. | Use of secure protocols (VPN, TLS, MPLS). |
| Right to Audit | Ensures vendor accountability. | Clauses allowing you to see their audit reports (e.g., SOC 2). |
| Incident Reporting | Vital for your own IR plan. | Requirement for the provider to notify you of a breach within X hours. |
Table of contents
- Key Takeaways: ISO 27001 Annex A 8.21 Security of Network Services
- What is ISO 27001 Annex A 8.21?
- ISO 27001 Annex A 8.21 Free Training Video
- ISO 27001 Annex A 8.21 Explainer Video
- ISO 27001 Annex A 8.21 Podcast
- ISO 27001 Annex A 8.21 Implementation Guidance
- How to implement ISO 27001 Annex A 8.21
- What to look for in your ISP Contract
- What will an auditor check?
- Applicability of ISO 27001 Annex A 8.21 across different business models.
- Fast Track 27001 Annex A 8.21 Compliance with the ISO 27001 Toolkit
- ISO 27001 Annex A 8.21 FAQ
- Related ISO 27001 Controls
- Further Reading
What is ISO 27001 Annex A 8.21?
ISO 27001 Annex A 8.21 is about the security of network services which means you need to define and agree your security requirements for network services.
ISO 27001 Annex A 8.21 Security of Network Services is an ISO 27001 control that requires us to secure our networks and have service levels and service requirements implemented, monitored and identified.
ISO 27001 Annex A 8.21 Purpose
ISO 27001 Annex A 8.21 is a preventive control to ensure security in the use of network services..
ISO 27001 Annex A 8.21 Definition
The ISO 27001 standard defines ISO 27001 Annex A 8.21 as:
Security mechanisms, service levels and service requirements of network services should be identified, implemented and monitored.
ISO27001:2022 Annex A 8.21 Security of Network Services
ISO 27001 Annex A 8.21 Free Training Video
In the video ISO 27001 Security of Network Services Explained – ISO27001:2022 Annex A 8.21 I show you how to implement it and how to pass the audit.
ISO 27001 Annex A 8.21 Explainer Video
In this beginner’s guide to ISO 27001 Annex A 8.21 Security of Network Services, ISO 27001 Lead Auditor Stuart Barker and his team talk you through what it is, how to implement in and how to pass the audit. Free ISO 27001 training.
ISO 27001 Annex A 8.21 Podcast
In this episode: Lead Auditor Stuart Barker and team do a deep dive into the ISO 27001:2022 Annex A 8.21 Security of Network Services. The podcast explores what it is, why it is important and the path to compliance.
ISO 27001 Annex A 8.21 Implementation Guidance
This control is looking for us to have control over our networks. We are going to ensure that we have identified what security measures we need, the service levels and the service requirements. Implementation is something that we can do internally or externally.
If external this is more about third party supplier management – see additional information:
ISO 27001 Annex A 5.19 Information Security In Supplier Relationships
ISO 27001 Annex A 5.20 Addressing Information Security Within Supplier Agreements
The standard wants us to monitor and and review the agreed service levels. A great element of the guidance is that it pushes us to consider third-party attestations to provide a demonstration that the service provider is maintaining appropriate security measures.
For me I would identify what the service requirements are then have a regular report and / or meeting that is set up to review it. I would keep evidence of this to show that I am managing it.
The are a few things to consider when it comes to what to cover so lets go through them. As we do it is worth noting that many of these are already covered and that the standard is making them specific here to networks.
Access to networks and services
For this we consider what can and should be accessed and then have appropriate policy and process in place around that access.
ISO 27001 Annex A 5.15 Access Control
ISO 27001 Annex A 5.18 Access Rights
Authentication
The requirements on authentication for accessing services should be set.
ISO 27001 Annex A 5.17 Authentication Information
Authorisation
Procedures that determine who is allowed to access networks and services are to be put in place.
ISO 27001 Annex A 5.15 Access Control
Technical Controls
The network management and technical controls as well as the processes to access connections and services will be in place.
ISO 27001 Annex A 8.20 Network Security
Access Types
How access is carried out such as physical network, wireless network, VPN will be determined.
Monitoring and Logging
Recording the time, location and other appropriate logging attributes of users that access networks and services will be in place.
ISO 27001 Annex A 8.16 Monitoring Activities
Security Features
The security features of networks will be identified and implemented as well as documented. Consider here things like encryption, connection controls, cacheing, restrictive access. Firewalls, private networks, intrusion detection are also to be considered.
Network Security Professional
All in all you should work what a network security professional to work out the best solution for you and your needs. Your requirement is to identify, document, implement, monitor and review it.
How to implement ISO 27001 Annex A 8.21
Securing network services is a vital requirement for ensuring the confidentiality and availability of data as it traverses both internal and external infrastructures. By following these technical steps, your organisation can effectively manage third-party service providers and internal network configurations to satisfy the rigorous standards of ISO 27001 Annex A 8.21.
1. Formalise Service Level Agreements and Security Requirements
- Document all security requirements within Service Level Agreements (SLAs) for every network service provider, including uptime guarantees and data protection obligations.
- Establish a “Rules of Engagement” (ROE) document that defines the technical boundaries and permissible actions for external service management.
- Result: Legally binding security baselines that ensure third-party providers adhere to your organisation’s internal risk posture.
2. Provision Secure Authentication and Encrypted Management Paths
- Mandate the use of Multi-Factor Authentication (MFA) for all administrative access to network service consoles and management interfaces.
- Enforce encrypted protocols such as SSHv2, SNMPv3, or TLS 1.3 for all remote management traffic to prevent credential sniffing and man-in-the-middle attacks.
- Result: Hardened administrative access that protects the integrity of network service configurations.
3. Restrict Service Access via Granular IAM Roles
- Implement the Principle of Least Privilege by assigning specific Identity and Access Management (IAM) roles to users and automated services based on their functional needs.
- Revoke generic or shared administrative credentials, ensuring all actions taken within network services are attributable to a specific verified identity.
- Result: A reduced attack surface where unauthorised users are blocked from modifying critical network service parameters.
4. Execute Continuous Monitoring and Logging of Network Services
- Configure all network services to export telemetry and audit logs to a centralised Security Information and Event Management (SIEM) platform.
- Establish automated alerts for “Unusual Service Modification” or “High-Frequency Access Failures” to detect potential compromise in real time.
- Result: Enhanced situational awareness and a comprehensive audit trail for both compliance verification and incident investigation.
5. Validate Service Integrity through Periodic Audits
- Conduct quarterly technical reviews of network service configurations to ensure they remain aligned with the documented security requirements.
- Perform vulnerability scans and penetration testing on service endpoints to identify and remediate weaknesses before they can be exploited.
- Result: A dynamic security posture that evolves to mitigate new threats targeting network service infrastructures.
6. Implement Traffic Filtering and Protection Mechanisms
- Deploy Web Application Firewalls (WAF) and Distributed Denial of Service (DDoS) protection to shield network services from application-layer attacks.
- Configure strict Network Access Control Lists (NACLs) to permit only authorised traffic flows between the service provider and the internal network.
- Result: Resilient network services capable of maintaining availability even during active targeted attacks.
What to look for in your ISP Contract
- Encryption: (Is the link encrypted? e.g., MPLS vs. VPN)
- Availability: (What is the uptime guarantee? 99.9%?)
- Data Separation: (Is my traffic separated from other customers?)
- Right to Audit: (Can we see their SOC 2 report?)
What will an auditor check?
The audit is going to check a number of areas. Lets go through the main ones
1. That you have documentation
What this means is that you need to show that you have documented your network, document your security implementation and put in place appropriate service levels.
2. That you have have implemented Security of Network Services appropriately
They will look at systems to seek evidence of that it is implement appropriately. They will want to see evidence of the controls that in place and that they are operating. Service levels will be expected to be in place and reviewed. Where you rely on third party attestation of the supplier then evidence of that will be expected to be shown.
3. That you have conducted internal audits
The audit will want to see that you have tested the controls and evidenced that they are operating. This is usually in the form of the required internal audits. They will check the records and outputs of those internal audits.
Applicability of ISO 27001 Annex A 8.21 across different business models.
| Business Type | Applicability | Examples of Control Implementation |
|---|---|---|
| Small Businesses | Focuses on the commercial agreement with the Internet Service Provider (ISP). It involves ensuring business-grade contracts are in place (not consumer lines) that guarantee fix-times and uptime. |
|
| Tech Startups | Applies to Cloud Network Services (e.g., AWS VPC, Cloudflare). Focus is on defining security features (WAF, DDoS protection) and monitoring them against the provider’s SLA. |
|
| AI Companies | Critical for high-bandwidth data pipelines. Requirements focus on guaranteed throughput for training data and low-latency SLAs for real-time inference APIs. |
|
Fast Track 27001 Annex A 8.21 Compliance with the ISO 27001 Toolkit
For ISO 27001 Annex A 8.21 (Security of network services), the requirement is to identify, implement, and monitor security mechanisms and service levels for your network services. This is a matter of supplier management and operational oversight, not a technical software problem that can be solved by an online platform.
| Compliance Factor | SaaS Network Service Monitoring | High Table ISO 27001 Toolkit | Real-World Example |
|---|---|---|---|
| Data Ownership & Continuity | Definitions of network service levels are “rented.” Stopping the subscription means losing the standards used to hold ISPs accountable. | Permanent Ownership: You receive the “Network Security Management Policy” and “Supplier Security Requirements” in Word/Excel formats that are yours forever. | Maintaining permanent records of your Service Level Agreements (SLAs) and security criteria without an ongoing bill. |
| Simplicity & Workflow | Over-engineers compliance by forcing you to link network circuits to a proprietary dashboard that ISPs will never see. | Accountability, Not Software: A “Network Services Security Checklist” integrates into existing procurement to check contracts for encryption and uptime. | Reviewing an ISP contract using a standard checklist rather than adding the administrative burden of a “compliance portal.” |
| Cost Structure | Often charges based on the number of “vendors” or “services” tracked, adding unnecessary expense for static documentation. | One-Off Fee: A single payment covers the documentation suite, whether you manage one ISP or a complex global network. | Managing a global network with ten different providers without increasing your compliance costs. |
| Freedom & Tech Agnostic | Rigid monitoring templates may struggle to adapt to modern cloud-first (AWS Direct Connect) or remote-first architectures. | Strategic Freedom: Fully editable policies allow you to define requirements for MPLS, VPNs, or cloud services exactly as you use them. | Switching from legacy MPLS to cloud-native network services without needing to reconfigure a rigid compliance tool. |
Summary: For Annex A 8.21, the auditor wants to see that you have identified security requirements for your network services and that you monitor them. The High Table ISO 27001 Toolkit provides the governance framework to do exactly that. It is the most direct, cost-effective way to prove you are managing your network services with permanent documentation that you own and control.
ISO 27001 Annex A 8.21 FAQ
What is ISO 27001 Annex A 8.21 Security of Network Services?
ISO 27001 Annex A 8.21 is a preventive control that requires organizations to identify, implement, and monitor security requirements for all network services. Unlike general network management, this control focuses specifically on the service levels and security mechanisms provided by third parties or internal teams to ensure business continuity and data protection.
- Scope: Covers ISPs, cloud connectivity, VPNs, and managed network services.
- Goal: To ensure network services are reliable, secure, and compliant with your organization’s specific needs.
- Key Action: Defining security requirements before signing contracts with service providers.
What is the difference between ISO 27001 Control 8.20 and 8.21?
Control 8.20 focuses on the technical infrastructure, whereas Control 8.21 focuses on the service delivery and management. While they are related, 8.20 handles the “plumbing” (routers, switches, firewalls), and 8.21 handles the commercial and operational “agreement” regarding how those services perform.
- Annex A 8.20 (Networks Security): Securing devices, segregating networks, and managing technical configurations.
- Annex A 8.21 (Security of Network Services): Managing SLAs, uptime guarantees, encryption standards, and vendor relationships.
- Integration: You need 8.20 to technically secure the network that delivers the services defined in 8.21.
What are the key requirements for complying with Annex A 8.21?
Compliance requires a three-step process: identification, implementation, and monitoring of service requirements. Organizations must stop treating network services as utilities and start managing them as critical security dependencies.
- Identify Requirements: Define necessary encryption levels, uptime targets (e.g., 99.9%), and data separation needs.
- Implement Agreements: Embed these requirements into Service Level Agreements (SLAs) or contracts.
- Monitor Performance: Regularly review service reports, audit logs, and uptime statistics to verify the provider is meeting their obligations.
What should be included in a Network Services SLA for ISO 27001?
A robust SLA must explicitly define security responsibilities, performance metrics, and the right to audit. Relying on standard provider contracts without review is a common compliance gap.
- Security Features: Specification of firewall management, DDoS protection, and encryption protocols (e.g., TLS, VPN).
- Service Levels: Guaranteed availability (uptime) and maximum acceptable latency.
- Incident Response: Mandatory notification windows if the provider suffers a security breach.
- Data Separation: Assurance that your traffic is logically isolated from other customers.
Does Annex A 8.21 apply to Cloud Services (AWS, Azure, Google Cloud)?
Yes, cloud connectivity and virtual network services are significantly in scope for Annex A 8.21. Modern organizations often rely more on cloud interconnects (like AWS Direct Connect or Azure ExpressRoute) than physical lines, making these relationships critical.
- Shared Responsibility: You must understand which network security controls the cloud provider handles vs. what you configure.
- SLA Review: Verify the cloud provider’s availability zones and failover guarantees meet your business continuity needs.
- Evidence: Download and review the provider’s SOC 2 Type II or ISO 27001 certificate as part of your monitoring process.
What evidence will an ISO 27001 auditor ask for regarding Control 8.21?
Auditors primarily seek evidence of governance, contract management, and ongoing monitoring. They want proof that you are actively managing your network providers rather than passively using them.
- Signed Contracts/SLAs: Documents highlighting security and availability clauses.
- Monitoring Records: Minutes from service review meetings or monthly uptime reports.
- Network Inventory: A list of all network services (ISPs, VPNs, SD-WAN) and their owners.
- Incident Logs: Records of any network outages and how the provider responded.
How often should network services be reviewed?
Network services should be reviewed at least annually or upon any significant contract renewal or architectural change. Continuous monitoring of automated reports should happen monthly.
- Annual Review: comprehensive check of the SLA against current business needs and risks.
- Monthly/Quarterly: Review of performance metrics (packet loss, uptime) provided by the vendor.
- Trigger-Based: Immediate review following a major incident or security breach at the provider.
Related ISO 27001 Controls
Further Reading
