A useful network boundary starts with an answer to why each connection exists.
Choose a service, not an entire address space
Begin with a business service whose owner can explain how it works. Record the application components and the people or systems that initiate connections. This keeps the first review understandable and creates a repeatable method for other services.
Include supporting services such as identity, name resolution, monitoring and backup. These dependencies are easy to miss when attention is limited to the main application.
Record the minimum useful detail
For each route, capture source, destination, service or protocol, business purpose, owner and evidence date. Identify whether the connection is permanent, occasional or required only for administration.
Traffic observations can help, but an observation period may miss month-end or disaster recovery activity. Ask the service owner about infrequent workflows before treating absence of traffic as proof that a route is unnecessary.
Make exceptions time-bound
Supplier support and project access often begin as temporary arrangements. Record why they are needed, who authorized them and what event should end them. An exception without an owner can outlive the original business purpose.
Where a legacy dependency cannot yet be removed, keep it visible in the design and agree a review date. The goal is an informed decision, not a misleading claim that every route is tightly restricted.
Use the register during change validation
Turn the approved connections into test cases. Confirm that legitimate tasks still work and that the intended boundaries are enforced. Keep rollback criteria available during the change window.
Update the register when systems change. See our Network Segmentation service for a structured way to map, prioritize and validate these boundaries.
Put the guidance into practice
Discuss the scope, responsibilities and evidence that would help your team make progress.
Understand a dependency before blocking its traffic
An application appears to communicate only with its database, but it also relies on name resolution, identity, monitoring and an external update service. A segmentation change based on an incomplete diagram can interrupt the business workflow. Start with a bounded service and combine configuration review, observed connections and discussion with its owner. Observation over a quiet period may miss scheduled or exceptional activities, so record the period examined and the gaps in the evidence.
Evidence to collect
- Identify source, destination, protocol, direction and business purpose for each relevant connection.
- Name the system owner and note whether the dependency is continuous, scheduled or exceptional.
- Separate observed connections from proposed or unverified requirements.
- Define an approved test, acceptance criteria and a way to reverse an unsuccessful change.
What a useful result looks like
Use the register to question unexplained paths and design a staged change. The aim is not to preserve every connection merely because it was observed: unwanted traffic also appears in logs. Confirm the business purpose and test the intended workflow after changes. Keep the register current when applications, suppliers or hosting arrangements change, and record exceptions with an owner and review date.
Is a network diagram enough?
A diagram is useful for orientation, but it may omit direction, timing, identity requirements and the reason for a connection. A register complements it with evidence and ownership. Neither replaces controlled testing of the proposed policy.