ID.AM-03: Representations of the organization’s authorized network communication and internal and external network data flows are maintained

ID.AM-03 is a practical requirement disguised as a documentation line item: if you cannot quickly explain how your network is allowed to communicate and how data is supposed to flow internally and externally, you will struggle to scope incidents, validate segmentation, govern third parties, and prove control operation. “Representations” means diagrams, maps, models, and structured inventories that a security operator can use to answer questions like: Which systems can talk to payroll? How does customer data exit our environment? Which third parties receive regulated data? Where are the choke points we monitor and log?

For a Compliance Officer, CCO, or GRC lead, the fastest path is to define what “authoritative” looks like, assign ownership, and connect the artifacts to operational workflows (architecture review, firewall rule approvals, cloud security reviews, vendor onboarding, and change management). You are not aiming for perfect network cartography. You are aiming for defensible, maintained representations that support risk decisions and can be validated against reality.

This page shows how to operationalize the id.am-03: representations of the organization’s authorized network communication and internal and external network data flows are maintained requirement with steps, evidence, and audit-ready habits, aligned to NIST CSF 2.0 (NIST CSWP 29; NIST CSF 1.1 to 2.0 Core Transition Changes).

Regulatory text

Requirement (verbatim excerpt): “Representations of the organization’s authorized network communication and internal and external network data flows are maintained” (NIST CSWP 29; NIST CSF 1.1 to 2.0 Core Transition Changes).

Operator interpretation of “must do”:

• Maintain current representations (not one-time diagrams) of:
  • Authorized network communication (who/what is permitted to connect to whom/what, over which channels).
  • Internal data flows (movement between internal systems, environments, and trust zones).
  • External data flows (movement to/from third parties, customers, and external services, including cloud/SaaS and integrations).
• Make them reviewable and governable: there should be an owner, a review cadence, a change trigger, and a way to track exceptions.

Plain-English interpretation

You need a reliable way to show:

1. what connections are allowed across your network, and
2. where your important data goes, especially when it crosses boundaries (internet, cloud, third parties, separate business units).

Auditors look for two properties: accuracy (can engineering validate it) and maintenance (does it stay updated as the environment changes).

Who it applies to

Entity scope: Any organization running a cybersecurity program that needs to manage systems, cloud services, and third-party connectivity under NIST CSF 2.0 (NIST CSWP 29).

Operational scope (where this becomes “real”):

• Hybrid networks: data center + cloud + SaaS.
• Environments with sensitive data (customer data, employee data, financial data, regulated data).
• High-change teams (DevOps, microservices, API ecosystems).
• Any organization with meaningful third-party integrations (payment processors, analytics, customer support platforms, managed service providers).

Teams you will need involved:

• Network/security engineering (firewalls, proxies, segmentation, routing)
• Cloud platform/DevOps (VPC/VNet, security groups, service meshes)
• Application owners (integration paths, APIs, queues)
• Data/analytics (ETL pipelines, data warehouses, BI tools)
• Third-party risk management and procurement (data sharing and connectivity)
• GRC (control definition, evidence, exceptions)

What you actually need to do (step-by-step)

Step 1: Define the minimum “representation set” (your audit baseline)

Create a short standard that specifies which artifacts count as your ID.AM-03 representations and what “maintained” means in your org (NIST CSWP 29).

A workable baseline set:

• Network communication representation
  • High-level network topology by environment (corp, prod, dev, DR).
  • Trust zone/segmentation diagram (zones and allowed paths).
  • “Allowed communications matrix” for critical systems (source, destination, port/protocol, purpose, enforcing control).
• Data-flow representation
  • Data flow diagrams for critical business services (ingest, process, store, transmit).
  • External data flow register (system → third party, data elements/categories, method: API/SFTP/webhook, encryption, owner).
  • Boundary map: where data leaves your control (SaaS, MSP, partners).

Practical decision: If you can’t map everything, start with “crown jewel” systems and regulated data flows first.

Step 2: Build an authoritative system and integration inventory

Representations fall apart if system names and owners are unclear. Establish:

• System list (production + supporting shared services)
• System owner and technical contact
• Hosting location (on-prem, cloud account/subscription, SaaS)
• Key inbound/outbound integrations
• Data classifications handled

This inventory becomes the index that diagrams reference. Without it, your diagrams become slideware.

Step 3: Document “authorized” communications, not just observed traffic

Auditors care about what is permitted by design and policy. Do both:

• Authorized-by-design
  • Approved architecture patterns (e.g., “apps may call DB only via private subnet”).
  • Firewall/security group intent: what should be open and why.
• Authorized-by-exception
  • Time-bound exceptions with compensating controls and approvals.

Then run a sanity check against what’s deployed (config exports, cloud security posture tooling, firewall rule review). Your representation should reconcile differences: fix the environment or update the authorization with documented approval.

Step 4: Map internal and external data flows with boundary crossings highlighted

For each critical service or dataset, capture:

• Sources (users, apps, batch feeds)
• Processing components (APIs, queues, functions, ETL jobs)
• Storage (databases, object stores, SaaS)
• Egress points (email, file transfer, API to third party, logging platforms)
• Security controls at each hop (TLS, encryption at rest, tokenization, DLP, IAM)

Make boundary crossings obvious. A reviewer should spot every point where data moves to a third party or public network in one pass.

Step 5: Tie maintenance to change management (this is the make-or-break)

“Maintained” requires triggers. Hardwire updates to workflows:

• New system onboarding requires an initial data-flow + network comms entry.
• Integration changes require updating the external flow register.
• Firewall/security group changes require updating the allowed communications matrix (or a reference to the approved ticket).
• Vendor onboarding requires confirming the data flow register entry matches the contract, DPIA, or security addendum.

If you already run CAB or SDLC gates, add “ID.AM-03 artifacts updated?” as an exit criterion.

Step 6: Assign owners and set review routines

Pick a control owner (often Enterprise Architecture, Security Architecture, or GRC with engineering sign-off). Define:

• Who updates diagrams (system owners)
• Who approves (security architecture)
• Who attests periodically (service owner + security)

Keep the routine lightweight: reviewers should confirm that flows still match reality and that exceptions are still justified.

Step 7: Centralize storage and versioning so you can prove history

Store artifacts in a controlled repo:

• Access controlled (read broadly, edit narrowly)
• Version history preserved
• Change log links to tickets/PRs
• Retention aligned to your audit needs

Many teams use a wiki plus a diagramming tool, but the critical requirement is governance: versioning, ownership, and auditability.

Required evidence and artifacts to retain

Auditors typically want evidence that the representations exist, are accurate enough to be relied upon, and are maintained.

Keep:

• Network topology and segmentation diagrams (current version + change history)
• Allowed communications matrix for in-scope systems (or per-zone)
• Data flow diagrams for critical services/datasets
• External data flow register (system → third party mapping)
• Inventory of systems/integrations with owners
• Change tickets/PRs showing updates to diagrams/registers tied to technical changes
• Review/attestation records (dated, by named approvers)
• Exception log for non-standard connections or flows (business justification, compensating controls, expiration)

Daydream fit (earned, not forced): If you struggle to keep evidence consistent across tools, Daydream can act as the control hub that maps ID.AM-03 to the policy, procedure, control owner, and recurring evidence collection so diagrams, registers, and review attestations stay connected during audits.

Common exam/audit questions and hangups

Expect questions like:

• “Show me where customer data flows externally, including SaaS and processors.”
• “Which systems can communicate with this database, and why is that authorized?”
• “How do you ensure the diagram stays current after cloud changes?”
• “Where are your boundary controls (firewall, WAF, proxies), and what flows traverse them?”
• “Prove that this third party integration is approved and monitored.”

Common hangups:

• Diagrams exist but are stale.
• Teams can’t distinguish “allowed” from “currently happening.”
• External flows are incomplete because SaaS is treated as “not network.”
• No exception governance for one-off firewall rules or temporary tunnels.

Frequent implementation mistakes and how to avoid them

Mistake	Why it fails	Avoid it by
Treating this as a one-time diagram project	The environment changes faster than documentation	Put updates behind change control gates and ownership
Mapping everything equally	You burn time and still miss risk	Start with crown jewels, regulated data, and internet/third-party boundaries
Only drawing topology, not flows	You can’t answer “what data leaves and how”	Maintain an external data flow register plus per-service flow diagrams
No approvals/attestations	Auditors see “nice pictures,” not governed controls	Record reviews, approvers, and exception decisions
External flows owned by nobody	Third-party integrations sprawl	Make system owners accountable for their outbound/inbound integrations

Enforcement context and risk implications

NIST CSF itself is a framework, not a regulator. Your exposure shows up indirectly: poor flow visibility leads to weak scoping during incidents, missed third-party data sharing, segmentation failures, and inability to demonstrate due care to customers, auditors, and regulators. If you operate in regulated sectors, expect this requirement to be tested through adjacent obligations (incident response scoping, data mapping, third-party oversight, and security architecture governance) (NIST CSWP 29).

Practical 30/60/90-day execution plan

First 30 days (stabilize the baseline)

• Name the control owner and approve a minimum “representation set.”
• Build the initial system/integration inventory for in-scope systems.
• Create the external data flow register template and populate the highest-risk third parties first.
• Publish a simple procedure: where artifacts live, who updates, who approves (NIST CSWP 29).

Days 31–60 (make it operational)

• Produce segmentation/trust zone diagrams for production and corporate networks.
• Build the allowed communications matrix for crown jewel systems.
• Add ID.AM-03 checks to change management: new systems, new integrations, firewall/security group changes.
• Stand up an exception workflow with expirations and compensating controls.

Days 61–90 (prove maintenance and auditability)

• Run a formal review cycle with service owner attestation and security sign-off.
• Reconcile “authorized” vs “observed” for a sample of critical flows; document remediation or approvals.
• Package an audit-ready evidence set: current artifacts, prior versions, review records, exceptions, and sample change tickets linked to updates.
• If evidence collection is scattered, connect the control to a system of record (for example, Daydream) to track ownership, evidence requests, and review completion.

Frequently Asked Questions

Do we need packet-level network flow logs to satisfy ID.AM-03?

No. The requirement is about maintained representations of authorized communication and data flows. Flow logs can help validate accuracy, but your core deliverable is governed diagrams/registers with approvals (NIST CSWP 29).

How detailed should the data flow diagrams be?

Detailed enough to identify boundary crossings, third parties, and security controls at transfer points. If a diagram can’t answer “where does sensitive data leave and through what mechanism,” it’s too high level.

Does SaaS count as an “external network data flow” even if it’s just a browser login?

Yes. If organizational data is accessed, processed, or stored in SaaS, you have an external data flow. Capture it in your external data flow register with the system owner, data categories, and transfer method.

We’re cloud-native; are security groups and routing tables our “authorized communications” evidence?

They are strong supporting evidence, but auditors still expect a human-readable representation that explains intent and scope. Keep diagrams/matrices that reference the underlying configurations and the approval trail.

Who should own ID.AM-03 in practice: GRC or Engineering?

Make one accountable owner (often Security Architecture or GRC), but require system owners to maintain their flows and require security to approve exceptions. Single-threaded accountability prevents stale artifacts.

What’s the fastest way to become audit-ready if we have nothing today?

Start with a crown jewel list, create an external data flow register, and document authorized communications for those systems only. Tie updates to change management immediately so the artifacts don’t decay after the first push.