This post explains, step-by-step, how to configure Nessus to discover and scan every networked device in your environment and produce the configuration and reporting evidence needed to meet NIST SP 800-171 Rev.2 / CMMC 2.0 Level 2 RA.L2-3.11.2.
Why RA.L2-3.11.2 matters and what auditors expect
Control RA.L2-3.11.2 focuses on vulnerability assessment configuration and reporting: organizations must routinely scan assets, use appropriately configured tools, and retain and present scan results and evidence demonstrating an ongoing program to identify and remediate vulnerabilities. Auditors expect a documented scan schedule, policy settings (credentialed vs. non-credentialed, plugin updates, safe checks), retained reports that map findings to remediation actions, and proof that all networked devices (servers, workstations, network gear, IoT) were included or intentionally excluded with justification.
Step 1 — Establish comprehensive asset discovery
Start by building an authoritative asset inventory: use Nessus Network Scan templates (or Tenable.sc if available) to run broad discovery on IP ranges and subnets. For small businesses with ~10–200 devices, run an initial ICMP/TCP port scan across RFC1918 networks and any internet-facing ranges. Complement network scans with Nessus Agents (or Tenable Cloud Agents) on machines that are behind NATs, on mobile devices, or otherwise unreachable. Example: a small business with 50 endpoints might run a single discovery scan for 10.0.0.0/24 and deploy agents to laptops that travel off-network. Save discovery output as CSV and import into your CMDB or spreadsheet for reconciliation.
Step 2 — Configure credentialed scans and device access
Credentialed scans dramatically improve coverage and reduce false positives. For Windows hosts enable SMB + WinRM (use a dedicated least-privileged service account with Logon as a service and local read access). For Linux use SSH key-based authentication with a non-root sudoer account. For network devices (switches/routers/firewalls) configure SNMP v3 or SSH access and add community strings or v3 credentials in Nessus. In the scan policy set appropriate port lists, increase SSH/SMB timeouts for slow devices, and whitelist any management VLANs to avoid false exclusions. Use agent scanning where credentials are impractical (IoT, BYOD) and schedule periodic agent check-ins to capture transient devices.
Step 3 — Tune scan policies and frequency for compliance
Create named policies that reflect compliance needs: "Internal Credentialed Weekly", "External Authenticated Monthly", and "Agent Continuous (Daily)". Enable these policy options: plugin updates before each scan, safe checks for production systems when necessary, and a vulnerability severity threshold for immediate alerts (e.g., Critical/High). Set concurrent host limits to avoid overwhelming small servers or network devices. For many small businesses a practical cadence is: agents run continuously (daily), internal credentialed scans run weekly, external-facing scans run monthly, and a full discovery scan runs quarterly. Document these cadences in your compliance plan and automate scan launches with the Nessus scheduler or the API.
Step 4 — Produce compliance-oriented reports and map findings
Nessus provides export formats (PDF, CSV, Nessus XML) and templates — build a "Compliance Evidence" PDF template that includes: scan name, start/end time, target list, credentials used (types, not passwords), plugin set and version, summary counts by severity, and a findings section with CVE IDs and remediation guidance. Map each finding to the relevant NIST/SP 800-171/CMMC control in the report (e.g., map missing MS patches to "3.11.2" remediation requirement). Keep raw exports (Nessus XML or CSV) as machine-readable evidence and store signed PDFs for auditors. Integrate with ticketing (Jira/ServiceNow) via Nessus API or Tenable.sc connectors so that each high/critical finding automatically opens a remediation ticket and includes scan IDs for traceability.
Practical small-business examples and implementation tips
Example 1: A 35-person consulting firm uses a single VM running Nessus Professional for internal scans and deploys Tenable Cloud Agents to employee laptops; they schedule weekly internal credentialed scans and monthly external scans, exporting a "Monthly Compliance Package" PDF for auditors. Example 2: A small manufacturing site has OT devices unreachable by credentials—use network discovery, SNMP polling for asset ID, and agent-based scans on gateways; add justification for non-credentialed OT scans in your POA&M with compensating controls (network segmentation, strict ACLs). Key tips: keep the Nessus plugin feed current (daily), use least-privilege scan accounts, exclude backups and high-risk production windows or use safe checks, and validate that scan windows and concurrency do not disrupt operations.
Risks of not implementing proper scanning and reporting
Failing to configure comprehensive Nessus scans and produce compliance-ready reports risks undetected vulnerabilities, successful exploitation of CUI, contractual penalties, and audit failures that can lead to lost contracts. For small businesses, a single unpatched RCE or exposed admin interface can lead to ransomware or data exfiltration. From a compliance perspective, lack of retained scan evidence or inconsistent scan configuration will almost certainly generate findings during a CMMC assessment and require POA&M entries with remediation timelines.
Summary: operationalize Nessus for RA.L2-3.11.2 compliance
To satisfy RA.L2-3.11.2, implement a repeatable Nessus program: discover all assets (network scans + agents), perform credentialed scans using dedicated least-privileged accounts, tune policies and schedule scans according to risk, and produce audit-ready reports that map findings to NIST SP 800-171/CMMC controls. Automate evidence collection (exports, ticket links, scan metadata), retain artifacts per your policy, and document any exclusions with compensating controls in your POA&M. Doing this not only meets compliance requirements but significantly reduces your security risk posture.
