In this ultimate how to audit guide to ISO 27001 Annex A 8.21 Security of Network Services, you will learn directly from an ISO 27001 Lead Auditor:
- 10 Key Audit Steps
- Verification Criteria
- Required Evidence
- The Pass / Fail Test
I am Stuart Barker, the ISO 27001 Lead Auditor and author of the Ultimate ISO 27001 Toolkit.
Using over 30 years of industry experience across hundreds of audits, I’m giving you the exact templates, walkthroughs, and practical examples you need to achieve ISO 27001 certification.
Table of contents
- 1. Network Service Level Agreement (SLA) Security Clause Verified
- 2. Network Service Security Feature Identification Confirmed
- 3. Secure Transmission Mechanism Enforcement Validated
- 4. Network Service Access Restriction Verified
- 5. Service Provider Security Monitoring Alignment Confirmed
- 6. DDoS Mitigation and Traffic Filtering Validated
- 7. Network Path Redundancy and Availability Confirmed
- 8. Service Provider Compliance Attestation Verified
- 9. Network Service Configuration Change Authorisation Validated
- 10. Secure Management of Virtual Network Services Confirmed
ISO 27001 Annex A 8.21 Security of Network Services Audit Checklist
Auditing ISO 27001 Annex A 8.21 Security of Network Services is the systematic evaluation of security controls applied to both internal and third-party networking. The Primary Implementation Requirement is robust service level agreements and encrypted transmission, providing the Business Benefit of ensuring continuous network reliability and integrity.
This technical verification tool is designed for auditors to establish the security integrity of internal and external network service agreements. Use this checklist to validate compliance with ISO 27001 Annex A 8.21.
1. Network Service Level Agreement (SLA) Security Clause Verified
Verification Criteria: All third-party network service agreements (ISPs, Cloud Providers, Managed Security Services) contain explicit information security requirements and service levels.
Required Evidence: Signed contracts or SLAs with highlighted security schedules and right-to-audit clauses.
Pass/Fail Test: If a network service is provided without a formal agreement specifying security obligations, mark as Non-Compliant.
2. Network Service Security Feature Identification Confirmed
Verification Criteria: The security features of all utilised network services (e.g. managed firewalls, VPNs, DDoS mitigation) are documented and aligned with the organisation’s risk appetite.
Required Evidence: Service catalogue or technical design document detailing the security controls provided by each network service.
Pass/Fail Test: If the organisation cannot define the specific security capabilities of a core network service (e.g. an unmanaged SD-WAN), mark as Non-Compliant.
3. Secure Transmission Mechanism Enforcement Validated
Verification Criteria: Technical controls ensure that all network services use secure, encrypted transmission protocols for data exchange (e.g. TLS 1.3, IPsec).
Required Evidence: Packet capture analysis, configuration logs, or cipher suite reports showing the rejection of insecure protocols (e.g. Telnet, HTTP, FTP).
Pass/Fail Test: If any network service allows the transmission of sensitive data over unencrypted channels, mark as Non-Compliant.
