NET-08: Separate Subnets To Isolate Functions
Mechanisms exist to implement physically or logically separate subnetworks to isolate organization-defined Technology Assets, Applications, Services and/or Data (TAASD).
Code reused: In SCF 2025.4 and earlier, NET-08 was Network Intrusion Detection / Prevention Systems (NIDS / NIPS). That control is now NET-31.
Control Question: Does the organization implement physically or logically separate subnetworks to isolate organization-defined Technology Assets, Applications, Services and/or Data (TAASD)?
General (2)
| Framework | Mapping Values |
|---|---|
| NIST 800-172 R3 | 03.13.09E 03.13.15E |
| NIST 800-172A R3 | A.03.13.09E.ODP[01] DS-A.03.13.15E A.03.13.15E.ODP[01] A.03.13.15E.ODP[02] |
US (1)
| Framework | Mapping Values |
|---|---|
| USA Federal DoW BaTB OT 2026 | 3 |
EMEA (2)
| Framework | Mapping Values |
|---|---|
| EMEA Israel CDMO 2.0 | Appendix A, 7.5 |
| EMEA Saudi Arabia OTCC-1 2022 | 2-4-1-1 2-4-1-5 2-4-1-6 2-4-1-9 2-4-1-10 2-4-1-12 2-4-1-13 |
Capability Maturity Model
Level 0 — Not Performed
Practices are non-existent, based on the inability to demonstrate an implemented and operational capability. A reasonable person would conclude the control is not being performed.
Level 1 — Performed Informally
Network Security (NET) domain capabilities are ad hoc and inconsistent. Capability criteria associated with this control may include: ▪ Policies, standards & procedures associated with NET domain capabilities provide limited coverage due to the depth and breadth of the existing documentation. ▪ Network security-related activities are decentralized (e.g., a localized/regionalized function) and uses non-standardized methods to implement secure, resilient and compliant practices.
Level 2 — Planned & Tracked
Identification & Authentication (IAC) capabilities are requirements-driven, but are not standardized across the entity (e.g., local/regional level consistency). Capability criteria associated with this control reasonably expect the following criteria to exist: ▪ Policies and standards associated with IAC domain capabilities are formally documented and centrally-managed by the entity. ▪ Standardized Operating Procedures (SOP) associated with IAC domain capabilities are documented and maintained by process owners. ▪ IT and/or cybersecurity personnel work with business stakeholders and process owners to appropriately scope and reasonably implement cybersecurity and data protection controls associated with IAC domain capabilities to address applicable statutory, regulatory and/or contractual requirements for Technology Assets, Applications, Services and/or Data (TAASD). ▪ Identity & Access Management (IAM)-related controls are primarily administrative and preventative in nature (e.g., policies, standards and procedures & guidelines) to enforce Logical Access Control (LAC). ▪ IAM may be a defined function (e.g., team or department) or assigned as an additional duty to existing IT and/or cybersecurity personnel to implement Role Based Access Control (RBAC) practices for the management of user, group and system accounts, including privileged accounts. ▪ A directory services technology is used to centrally manage identities and permissions with RBAC. Due to technical or business limitations, asset/process owners are empowered to operate a decentralized access control program for their specific Technology Assets, Applications and/or Services (TAAS) that cannot be integrated into directory services.
Level 3 — Well Defined
Network Security (NET) capabilities are standardized across the entity for applicability to People, Processes, Technologies, Data and/or Facilities (PPTDF) to ensure consistency for Technology Assets, Applications, Services and/or Data (TAASD). Capability criteria associated with this control reasonably expect the following criteria to exist: ▪ Policies and standards associated with NET domain capabilities are formally documented and centrally-managed by the entity's Governance, Risk & Compliance (GRC) team, or similar function. ▪ Standardized Operating Procedures (SOP) associated with NET domain capabilities are well-documented and kept current by process owners. ▪ A network security management team, or similar function, is appropriately staffed and supported to implement and maintain NET domain capabilities. ▪ Technology is leveraged to enhance the efficiency and accuracy of network security operations (e.g., network management solution and log aggregator). ▪ The entity's Governance, Risk & Compliance (GRC) team, or similar function, works with business stakeholders and process owners to appropriately scope and reasonably implement cybersecurity and data protection controls associated with NET domain capabilities to address Minimum Compliance Requirements (MCR) (e.g., applicable statutory, regulatory and/or contractual requirements) and Discretionary Security Requirements (DSR) (e.g., entity-required controls). ▪ Secure Baseline Configurations (SBC) enforce the principles of least privileges and least functionality for boundary protection technologies. ▪ An implemented and operational capability exists to implement physically or logically separate subnetworks to isolate organization-defined Technology Assets, Applications, Services and/or Data (TAASD).
Level 4 — Quantitatively Controlled
Utilize SCR-CMM Level 3 criteria definitions: ▪ There are no defined Level 4 criteria, since it is reasonable to assume a quantitatively-controlled process is not necessary to operationalize this control. ▪ While it may be possible to develop “metrics-driven” capabilities for this control, the criteria would be organization-specific to define.
Level 5 — Continuously Improving
Utilize SCR-CMM Level 3 or Level 4 (if available) criteria definitions: ▪ There are no defined Level 5 criteria, since it is reasonable to assume a continuously-improving process is not necessary to operationalize this control. ▪ Level 5 capabilities should be considered “world-class” where the control builds on Level 4 capabilities, but are continuously improving through Artificial Intelligence (AI) and/or Machine Learning (ML) technologies. ▪ While it may be possible to develop responsive capabilities for this control through the use of AI and/or ML technologies, the criteria would be organization-specific to define.
Assessment Objectives
- NET-08_A01 subnetworks are physically or logically separate to isolate organization-defined Technology Assets, Applications, Services and/or Data (TAASD).
Evidence Requirements
- E-NET-08 Internal Boundaries
-
Documented evidence of key internal boundaries.
Network Security
Technology Recommendations
Micro/Small
- Subnetting for basic functional isolation
- VLAN segmentation
Small
- VLAN-based subnet isolation
- Separate subnets for servers, workstations and IoT/OT
Medium
- Subnet-based micro-segmentation
- Firewall rules between functional subnets
- Network ACLs for inter-subnet traffic
Large
- Network micro-segmentation
- Host-based firewall enforcement between subnets
- Zero Trust Network Architecture (ZTNA) between segments
Enterprise
- Enterprise micro-segmentation platform (e.g., Illumio, Guardicore)
- Software-Defined Networking (SDN) for subnet isolation
- ZTNA platform for workload-to-workload access control
- Automated subnet policy enforcement