ISO/IEC 27001:2022 Annex A · Control 8.20

Network Security: A Practical Implementation Guide

Design, configure and monitor networks to protect information and connected services.

This control concerns securing and managing networks and network devices to protect information in systems and applications.

Practical interpretation: Network security spans architecture, device hardening, routing, access, encryption, monitoring, resilience and operational ownership across on-premises and cloud.

What should the control achieve?

Network architecture and trust boundaries are documented.
Devices follow secure baselines.
Traffic is restricted and monitored.
Changes and incidents are controlled.

Step-by-step implementation

Map architecture

Document zones, routes, external links, cloud networks, remote access and critical flows.

Define trust boundaries

Apply default-deny principles and controlled ingress, egress and management.

Harden infrastructure

Secure protocols, administration, configuration, updates and backups.

Protect communications

Use encryption and authenticated tunnels according to risk.

Monitor traffic and devices

Collect flow, firewall, DNS and device logs and detect anomalies.

Test and review

Assess rules, exposure, resilience and unauthorized paths.

What this could look like in practice

A hybrid network separates user, production, management and guest zones. Administrative access uses a hardened jump path, firewall rules map to approved applications and quarterly reviews remove unused rules.

Activity	Practical implementation	Evidence
Architecture	Zones and data flows are documented.	Network diagram
Rule change	Owner and Network Security approve justified flow.	Change ticket
Administration	MFA and management network protect devices.	Admin log
Monitoring	Anomalous egress creates investigation.	Alert case

Implementation evidence

Network security standard
Current diagrams
Device inventory
Configuration baselines
Firewall rules
Change records
Network logs
Rule reviews

Useful metrics

Unreviewed firewall rules
Internet-exposed services
Network devices below baseline
Unauthorized paths found

Common mistakes

Flat networks.
Any-to-any rules.
Managing devices through insecure protocols.
Outdated diagrams.
Ignoring cloud and third-party connectivity.

Questions an auditor may ask

Where are trust boundaries?
How are network rules approved?
Show secure device administration.
How is unexpected traffic detected?

Implementation test: Trace critical and prohibited traffic across zones and verify routing, enforcement, logging and review.

Continue through Annex A

Explore the growing library of practical guides for all 93 Annex A controls.

Open the ISO 27001 Annex A Control Library

This independent educational guide paraphrases the practical intent of the control and does not replace the official ISO standards, professional advice or an organization-specific risk assessment. It is not affiliated with or endorsed by ISO.

ISO 27001 Annex A 8.20: Network Security – Practical Implementation Guide