A.8.21·high·Component: Technological controlsWhat this control requires
Security mechanisms, service levels and service requirements of network services shall be identified, implemented and monitored.
In plain English
Security mechanisms, service levels and service requirements of network services shall be identified, implemented and monitored. In practice, this means you can prove you management management-level controls on a defined cadence.
Why it matters
ISO 27001 certification depends on showing each Annex A control is either implemented or explicitly justified for exclusion in the Statement of Applicability (SoA). Certification bodies sample controls during surveillance audits, and a missing SoA entry — or implementation that doesn't match the SoA wording — is a finding.
This control is rated high. Auditors expect a named owner, a remediation SLA, and a tooling artefact that evidences continuous operation.
What an auditor looks for
An ISO 27001 lead auditor looks for: (1) an SoA entry covering the control with justification, (2) a documented procedure or policy implementing it, (3) records that prove the procedure runs (logs, tickets, training records) and (4) management-review evidence that effectiveness is monitored.
Within Technological controls, the assessor will trace your implementation back to the catalogue reference (Annex A A.8.21) and look for objective evidence on the latest two assessment cycles.
How to implement
Cloud Posture
CSPM. Run Wiz / Prisma / Defender for Cloud / Security Command Center over every account; auto-ticket findings above your accepted-risk threshold.
Network Security
AWS. VPC Flow Logs to S3, default-deny security groups, AWS Network Firewall for north-south, and Transit Gateway for hub-and-spoke segmentation.
Azure. NSGs with deny-by-default, Azure Firewall Premium with TLS inspection, Private Endpoints for PaaS, and Microsoft Defender for Cloud's secure score for drift.
GCP. VPC Service Controls perimeters around sensitive APIs, Cloud NGFW Enterprise for L7 inspection, Private Service Connect for managed services.
Operational checklist
- Management. Document the trigger, the owner and the cadence.
- Security. Document the trigger, the owner and the cadence.
- Scope: management, security, services, network services.
Evidence to collect
- Infra Scan. Continuous infrastructure-posture telemetry — AWS Config, Azure Policy compliance, GCP Organisation Policy, Wiz / Prisma findings.
Infrastructure security scans (AWS Config, Azure Policy) verify network services meet defined control baselines.
Common pitfalls
- Treating CSPM findings as a backlog instead of a hot queue: findings older than the policy SLA accumulate until the auditor asks why.
- Default-allow egress rules; East-West traffic with no segmentation; jump hosts on the public internet with password auth.
How it maps to other frameworks
Computed from shared tags, control component and key-operation subjects — handy when you are reconciling controls across an audit.
- NIST SP 800-171 Rev. 3 3.13.6 — Network Communications - Deny by Default - Allow by Exception
- CIS Controls v8 12.5 — Centralize Network Authentication, Authorization, and Auditing (AAA)
- NIST SP 800-53 Rev. 5 CM-7 — Least Functionality
- BSI C5:2020 COS-07 — Documentation of the network topology
Related controls in ISO/IEC 27001:2022
- Annex A A.8.22 — Segregation of networks
- Annex A A.5.23 — Information security for use of cloud services
- Annex A A.5.34 — Privacy and protection of personal identifiable information (PII)
- Annex A A.8.24 — Use of cryptography
References
- ISO/IEC JTC 1/SC 27 — ISO/IEC 27001:2022
- Catalogue identifier:
Annex A A.8.21
Topics: network securitycloud posturecertificate managementencryption in transit