6.8 Network segmentation

Requirement

The relevant entities shall segment systems into networks or zones in accordance with the results of the risk assessment referred to in point 2.1. They shall segment their systems and networks from third parties’ systems and networks.

Guidance

• Take into account well known standards when segmenting networks (66).
• Integrate the segmentation derived from the risk assessment into the network diagram.

Examples of evidence

• Documented network segmentation rules based on relevant standards and good practices.

GUIDANCE 67, 68

• Make sure that the segments are in line with the results of the risk assessment (Annex to the regulation, point 2.1).
• Apply a graduated set of measures in different logical network domains to further segregate the network security environments, including:
  • publicly accessible systems;
  • internal networks;
  • OOB connections; and
  • assets with high criticality.
• Implement subnetworks for publicly accessible system components that are physically and/or logically separate from internal organisational networks.
• Determine the degree of physical separation of system components from physically distinct components:
  • in separate racks in the same room,
  • in separate rooms for the components with high criticality and
  • more significant geographical separation of the components with high criticality.
• Implement separate network addresses (that is,, different subnets) to connect to systems in different security domains.
• Monitor and control communications at the external boundary of the system as well as at key internal boundaries within the system, including segmentation violations.
• Where appropriate, isolate information security tools, mechanisms and support components from other internal information system components, where appropriate (69), by implementing physically separate subnetworks with managed interfaces to other components of the system.
• Route all networked, privileged accesses through a dedicated, managed interface for the purposes of access control and auditing.
• Implement a managed interface for each external telecommunication service.

Requirement

For that purpose, the relevant entities shall: (a) consider the functional, logical and physical relationship, including location, between trustworthy systems and services; (b) grant access to a network or zone based on an assessment of its security requirements; (c) keep systems that are critical to the relevant entities operation or to safety in secured zones; (d) deploy a demilitarised zone within their communication networks to ensure secure communication originating from or destined to their networks; (e) restrict access and communications between and within zones to those necessary for the operation of the relevant entities or for safety; (f) separate the dedicated network for administration of network and information systems from the relevant entities’ operational network; (g) segregate network administration channels from other network traffic;

(h) separate the production systems for the relevant entities’ services from systems used in development and testing, including backups.

Examples of evidence

• Risk assessments that justify the segmentation decisions.
• Interviews with IT and security staff to understand the rationale behind network segmentation.
• Up-to-date network diagrams showing segmentation into different networks or zones (e.g. DMZ (70), internal networks and guest networks).
• Verification that the diagrams align with business functions and risk profiles.
• Documented criteria for creating and maintaining different network zones.
• VLAN configurations on network switches and routers.
• VLANs corresponding to different security zones and business functions.
• Measures (e.g. IDS/IPS and monitoring systems) tailored to each network zone.
• Configurations of network devices (e.g. routers, switches and firewalls) for appropriate segmentation settings.
• Configuration settings that match documented segmentation rules and diagrams.
• ACLs that consider segregation of duties.
• Firewall configurations.

Requirement

The relevant entities shall review and, where appropriate, update network segmentation at planned intervals and when significant incidents or significant changes to operations or risks.

Guidance

• Review and, if necessary, update the process for network segmentation rules at least annually.

Examples of evidence

• Reports from recent penetration tests and/or vulnerability scans.
• Plans or schedules for reviewing network segmentation rules.
• Logs or records confirming that the reviews have been conducted in accordance with the schedule.
• Change management documentation for network segmentation changes, in line with risk-assessment results and business needs.
• Incident response documentation to verify that network segmentation rules are reviewed following significant security incidents.
• Post-incident analysis reports that include assessments of segmentation rule effectiveness and any necessary adjustments.
• Internal or external audit logs and reports that cover network segmentation rule reviews.
• Reviews performed periodically and in response to network changes or incidents.
• Minutes from security or IT operations meetings where network segmentation rules are discussed.
• Penetration tests and vulnerability assessments that include evaluations of network segmentation.
• Tests conducted periodically and after major changes or incidents and findings leading to rule reviews.

Tips: guidance

• Limit the data traffic between the different segments to the operationally required extent by means of data flow control for example a firewall.
• Connect to external networks or information systems only through managed interfaces consisting of boundary protection devices arranged in accordance with the entity’s security architecture such as:
  • gateways;
  • routers;
  • firewalls;
  • network-based malicious code analysis;
  • virtualisation systems; and
  • encrypted tunnels.
• Prevent discovery of specific system components composing a managed interface.
• Monitor exceptions.

Tips: examples of evidence

• Network isolation and implementation of segmented network security zones that limit the impact of a malicious software incident.
• Logging and monitoring active for each zone.
• Alerts for segmentation rule violations.
• Reviews triggered by alerts to segmentation violations.