This post explains how to implement access control measures—specifically Active Directory (AD) configuration, multi-factor authentication (MFA), and network segmentation—to satisfy FAR 52.204-21 and CMMC 2.0 Level 1 control AC.L1-B.1.I within the Compliance Framework context, focusing on practical steps, small-business scenarios, and auditor evidence requirements.
\n\nCompliance Framework (as applied to FAR 52.204-21 / CMMC 2.0 Level 1) expects organizations to limit information system access to authorized users, manage accounts using least privilege, and reduce exposure of Controlled Unclassified Information (CUI). Practically this means: (1) centralize identity management with AD or Azure AD, (2) enforce MFA on remote and privileged access, and (3) segment networks so that systems that store or process CUI are isolated and only reachable by explicitly authorized endpoints and users.
\n\nStart with an inventory and baseline: list OUs, groups, service accounts, privileged accounts, and joining status for all endpoints. Create OUs that map to administrative tiers (e.g., Tier 0: Domain Controllers and AD admins; Tier 1: servers processing CUI; Tier 2: user workstations). Use group-based delegation instead of direct user assignments—create security groups for application access and admin tasks, then assign group membership through a documented change-control process.
\n\nImplement AD security settings via Group Policy (GPO): set password policy (minimum 12 characters, history 24, maximum password age 60–90 days depending on risk tolerance), account lockout (e.g., 5 invalid attempts, 15-minute lockout), and enable LAPS (Local Administrator Password Solution) to manage local admin passwords per machine. For hybrid environments, use Azure AD Connect with selective sync: only sync identities needed in Azure AD, enable password hash sync or pass-through authentication, and ensure \"writeback\" features (password reset) are configured if you want self-service password reset. Document service accounts and convert high-privilege accounts to managed service accounts (gMSA) where possible to remove static credentials.
\n\nA 25-user company can implement a simple yet compliant design: single forest with two OUs (Workstations and Servers), AD groups like \"Finance-CUI-Access\" and \"IT-Admins\", GPOs for password and lockout, and LAPS for local admin. Use a jump-host for any server administration and require membership in \"IT-Admins\" for RDP access to the jump-host. Keep AD admin accounts off the internet (do not use them to log into mail or web) to reduce credential phishing risk.
\n\nMFA is required for remote access and privileged operations. For cloud services, enforce Azure AD Conditional Access policies: require MFA for all users accessing Office 365, admin roles, and external access. Example policy: apply to \"All cloud apps\" and \"All users\" except a monitored break-glass account; grant control: Require multi-factor authentication. For on-prem resources (VPN, RD Gateway, RDP exposed via Bastion), use your VPN/rd-gateway vendor's MFA integration (Duo, Okta, Azure MFA NPS extension). For small shops without cloud identity, use an MFA solution that integrates with Active Directory Federation Services (AD FS) or deploy a third-party RADIUS/NPS MFA adapter.
\n\nDesign segmentation by trust and function: separate guest Wi‑Fi, employee workstations, administrative hosts, servers holding CUI, and DMZ services. At minimum implement VLANs with inter-VLAN firewall rules that follow \"deny by default, allow explicitly\"—only open ports required for business (e.g., 443 to web servers, 3389 only to jump hosts). For a small business, use a business-class firewall (with zone-based policy) and create rules such as: allow 10.0.1.0/24 (workstations) to 10.0.2.10 (app server) on TCP/443; deny all other traffic between VLANs. Consider host-based controls (Windows Firewall via GPO) and NAC (network access control) or certificate-based device authentication to prevent unmanaged devices from joining CUI VLANs.
\n\nAuditors will want artifacts: AD group membership exports, GPO settings (password policy, account lockout, LAPS deployment status), Conditional Access/MFA policy screenshots, VPN or RD Gateway MFA configuration, network diagrams showing VLANs and ACLs, and firewall rule exports. Collect logs that show MFA events and access attempts—e.g., Azure AD sign-in logs, VPN auth logs, firewall allow/deny logs—and store them for the retention period required by your contract. Automate evidence collection where possible: schedule exports of group membership and Conditional Access policies, and keep a change-control ticket linked to each access change.
\n\nFailing to implement AD hardening, MFA, and segmentation increases the risk of credential compromise, lateral movement, and CUI exfiltration. Consequences include contract termination, loss of future contracting opportunities, and regulator or prime-contractor penalties. Best practices: enforce least privilege, use Privileged Access Workstations (PAWs) for admin tasks, maintain break-glass accounts with time-limited access and offline MFA, rotate and manage service account credentials, perform periodic access reviews, and implement endpoint detection (EDR) to detect lateral movement attempts.
\n\nIn summary, meeting FAR 52.204-21 / CMMC 2.0 Level 1 AC.L1-B.1.I is achievable for small businesses by combining well-configured Active Directory (or Azure AD hybrid), enforced MFA for remote and privileged access, and clear network segmentation that limits access to CUI. Build simple, documented configurations, collect the required evidence (policies, logs, diagrams), and run periodic audits and tests (penetration or tabletop exercises) to validate your controls and maintain a defensible compliance posture.
", "plain_text": "This post explains how to implement access control measures—specifically Active Directory (AD) configuration, multi-factor authentication (MFA), and network segmentation—to satisfy FAR 52.204-21 and CMMC 2.0 Level 1 control AC.L1-B.1.I within the Compliance Framework context, focusing on practical steps, small-business scenarios, and auditor evidence requirements.\n\nObjectives and what Compliance Framework expects\nCompliance Framework (as applied to FAR 52.204-21 / CMMC 2.0 Level 1) expects organizations to limit information system access to authorized users, manage accounts using least privilege, and reduce exposure of Controlled Unclassified Information (CUI). Practically this means: (1) centralize identity management with AD or Azure AD, (2) enforce MFA on remote and privileged access, and (3) segment networks so that systems that store or process CUI are isolated and only reachable by explicitly authorized endpoints and users.\n\nConfiguring Active Directory (on-prem and hybrid)\nStart with an inventory and baseline: list OUs, groups, service accounts, privileged accounts, and joining status for all endpoints. Create OUs that map to administrative tiers (e.g., Tier 0: Domain Controllers and AD admins; Tier 1: servers processing CUI; Tier 2: user workstations). Use group-based delegation instead of direct user assignments—create security groups for application access and admin tasks, then assign group membership through a documented change-control process.\n\nImplement AD security settings via Group Policy (GPO): set password policy (minimum 12 characters, history 24, maximum password age 60–90 days depending on risk tolerance), account lockout (e.g., 5 invalid attempts, 15-minute lockout), and enable LAPS (Local Administrator Password Solution) to manage local admin passwords per machine. For hybrid environments, use Azure AD Connect with selective sync: only sync identities needed in Azure AD, enable password hash sync or pass-through authentication, and ensure \"writeback\" features (password reset) are configured if you want self-service password reset. Document service accounts and convert high-privilege accounts to managed service accounts (gMSA) where possible to remove static credentials.\n\nSmall business example: 25-employee company\nA 25-user company can implement a simple yet compliant design: single forest with two OUs (Workstations and Servers), AD groups like \"Finance-CUI-Access\" and \"IT-Admins\", GPOs for password and lockout, and LAPS for local admin. Use a jump-host for any server administration and require membership in \"IT-Admins\" for RDP access to the jump-host. Keep AD admin accounts off the internet (do not use them to log into mail or web) to reduce credential phishing risk.\n\nImplementing MFA: selection and configuration\nMFA is required for remote access and privileged operations. For cloud services, enforce Azure AD Conditional Access policies: require MFA for all users accessing Office 365, admin roles, and external access. Example policy: apply to \"All cloud apps\" and \"All users\" except a monitored break-glass account; grant control: Require multi-factor authentication. For on-prem resources (VPN, RD Gateway, RDP exposed via Bastion), use your VPN/rd-gateway vendor's MFA integration (Duo, Okta, Azure MFA NPS extension). For small shops without cloud identity, use an MFA solution that integrates with Active Directory Federation Services (AD FS) or deploy a third-party RADIUS/NPS MFA adapter.\n\nNetwork segmentation and microsegmentation\nDesign segmentation by trust and function: separate guest Wi‑Fi, employee workstations, administrative hosts, servers holding CUI, and DMZ services. At minimum implement VLANs with inter-VLAN firewall rules that follow \"deny by default, allow explicitly\"—only open ports required for business (e.g., 443 to web servers, 3389 only to jump hosts). For a small business, use a business-class firewall (with zone-based policy) and create rules such as: allow 10.0.1.0/24 (workstations) to 10.0.2.10 (app server) on TCP/443; deny all other traffic between VLANs. Consider host-based controls (Windows Firewall via GPO) and NAC (network access control) or certificate-based device authentication to prevent unmanaged devices from joining CUI VLANs.\n\nEvidence, monitoring, and validation for auditors\nAuditors will want artifacts: AD group membership exports, GPO settings (password policy, account lockout, LAPS deployment status), Conditional Access/MFA policy screenshots, VPN or RD Gateway MFA configuration, network diagrams showing VLANs and ACLs, and firewall rule exports. Collect logs that show MFA events and access attempts—e.g., Azure AD sign-in logs, VPN auth logs, firewall allow/deny logs—and store them for the retention period required by your contract. Automate evidence collection where possible: schedule exports of group membership and Conditional Access policies, and keep a change-control ticket linked to each access change.\n\nRisks of not implementing the requirement and best practices\nFailing to implement AD hardening, MFA, and segmentation increases the risk of credential compromise, lateral movement, and CUI exfiltration. Consequences include contract termination, loss of future contracting opportunities, and regulator or prime-contractor penalties. Best practices: enforce least privilege, use Privileged Access Workstations (PAWs) for admin tasks, maintain break-glass accounts with time-limited access and offline MFA, rotate and manage service account credentials, perform periodic access reviews, and implement endpoint detection (EDR) to detect lateral movement attempts.\n\nIn summary, meeting FAR 52.204-21 / CMMC 2.0 Level 1 AC.L1-B.1.I is achievable for small businesses by combining well-configured Active Directory (or Azure AD hybrid), enforced MFA for remote and privileged access, and clear network segmentation that limits access to CUI. Build simple, documented configurations, collect the required evidence (policies, logs, diagrams), and run periodic audits and tests (penetration or tabletop exercises) to validate your controls and maintain a defensible compliance posture." }, "metadata": { "description": "Practical, step-by-step guidance for configuring Active Directory, multi-factor authentication, and network segmentation to meet FAR 52.204-21 / CMMC 2.0 Level 1 (AC.L1-B.1.I) requirements for small and mid-sized businesses.", "permalink": "/how-to-use-access-control-tools-to-meet-far-52204-21-cmmc-20-level-1-control-acl1-b1i-configuring-ad-mfa-and-network-segmentation.json", "categories": [], "tags": [] } }