---
title: "NIST 800-171 3.1.20 (AC.L2-3.1.20): External Connections"
description: "NIST SP 800-171 3.1.20 External Connections: 1 SPRS point, never on a CMMC POA&M. The text, what assessors check and the evidence."
url: https://policycortex.com/nist-800-171/access-control/3.1.20
sealed: 2026-11-11
amended: 2026-11-11
register: nist-800-171/access-control/3.1.20
records: 7
digest: sha3:e817b84d9583fbd73e8bf7f27ef459d9bad08cc1b7ec173b98b382e2a9568817
---

# NIST 800-171 3.1.20 (AC.L2-3.1.20): External Connections

NIST 800-171 / Access Control / 3.1.20

"Verify and control/limit connections to and use of external systems." ([NIST SP 800-171 Rev. 2, requirement 3.1.20](https://doi.org/10.6028/NIST.SP.800-171r2))

CMMC Level 2 practice AC.L2-3.1.20.

## What 3.1.20 means in practice

External systems are ones you do not control, such as personal devices, a partner's network or a cloud service outside your boundary. List the external systems that connect to or are used with your system, verify their security before allowing the connection, and set terms that limit what may be done with them.

## SPRS points and the CMMC POA&M

- **CMMC Level 2 practice**: AC.L2-3.1.20
- **SPRS points**: 1 point. When it is not met, the DoD Assessment Methodology subtracts 1 from the score of 110.
- **CMMC POA&M**: Never. 32 CFR 170.21(a)(2)(iii) names 3.1.20 among the 6 requirements a CMMC POA&M may never include, whatever their point value.

Sources: [NIST SP 800-171 DoD Assessment Methodology, version 1.2.1 (June 24, 2020), Annex A](https://www.acq.osd.mil/asda/dpc/cp/cyber/docs/safeguarding/NIST-SP-800-171-Assessment-Methodology-Version-1.2.1-6.24.2020.pdf); [32 CFR 170.21, Plan of Action and Milestones requirements](https://www.ecfr.gov/current/title-32/section-170.21).

## What an assessor checks for 3.1.20

NIST SP 800-171A gives 6 determination statements for 3.1.20, each found satisfied or other than satisfied. Determine if:

- 3.1.20[a] connections to external systems are identified.
- 3.1.20[b] the use of external systems is identified.
- 3.1.20[c] connections to external systems are verified.
- 3.1.20[d] the use of external systems is verified.
- 3.1.20[e] connections to external systems are controlled/limited.
- 3.1.20[f] the use of external systems is controlled/limited.

[NIST SP 800-171A (June 2018), assessment objectives for 3.1.20](https://doi.org/10.6028/NIST.SP.800-171A)

## Evidence that shows 3.1.20 is met

- An inventory of the external systems and cloud services that connect to or are used with the system.
- Agreements or terms of use for each, with the security review or FedRAMP authorization relied on.
- Configuration that blocks unapproved external connections, such as personal devices or unsanctioned cloud applications.

## How PolicyCortex gathers the evidence

No PolicyCortex collector reads the evidence for 3.1.20. Your team provides the evidence listed above.

## Related pages

- **Calculator**: [SPRS score calculator: mark 3.1.20 and the other 109 requirements and see the score.](https://policycortex.com/sprs-score-calculator#family-AC)
- **Sample package**: [Sample package: an SSP, a POA&M and an evidence chain the product generated from demonstration data.](https://policycortex.com/sample-package)
- **Family**: [All 22 Access Control requirements (3.1).](https://policycortex.com/nist-800-171/access-control)
- **Previous**: [3.1.19: Encrypt CUI on Mobile](https://policycortex.com/nist-800-171/access-control/3.1.19)
- **Next**: [3.1.21: Portable Storage Use](https://policycortex.com/nist-800-171/access-control/3.1.21)
- **All requirements**: [All 110 NIST SP 800-171 requirements, by family.](https://policycortex.com/nist-800-171)

Meet the requirement once. Keep the evidence current. [Request Access](https://app.policycortex.com/auth?mode=request-access) · [Book a call](https://policycortex.com/book)

## Register colophon

| Seq | Label | SHA3-256 | Prev |
|---|---|---|---|
| REC 0000 | REQUIREMENT | 47781632f30d | 3bbc10617ce9 |
| REC 0001 | MEANING | edc01f23af92 | 47781632f30d |
| REC 0002 | POINTS AND POA&M | 7324aafa4bb4 | edc01f23af92 |
| REC 0003 | ASSESSMENT OBJECTIVES | 72eeee6e063f | 7324aafa4bb4 |
| REC 0004 | EVIDENCE | b8abc11f2912 | 72eeee6e063f |
| REC 0005 | COLLECTORS | 229b88dcd71f | b8abc11f2912 |
| REC 0006 | RELATED | e817b84d9583 | 229b88dcd71f |

Head sha3:e817b84d9583fbd73e8bf7f27ef459d9bad08cc1b7ec173b98b382e2a9568817. Each digest is SHA3-256 over the previous digest, the register key, the record label, and the record copy; a second party can recompute it from this document.