Change Inputs
Example Change Log
| Change | Scope | Env | Testing | Rollback | Impact Score | Band |
|---|---|---|---|---|---|---|
| Add allow rule for partner API | 2 subnets, 2 ports, TCP | Staging | 70% | Yes | 41 | Medium |
| Modify inbound rule for payroll | 8 subnets, 6 ports, TCP/UDP | Production | 55% | Yes | 68 | High |
| Delete legacy deny rule | 1 subnet, 1 port, TCP | Production | 30% | No | 82 | Critical |
Formula Used
The calculator produces four sub-scores on a 0–100 scale and combines them into an overall impact score. Inputs are normalized and clamped to keep results stable across different network sizes.
How to Use This Calculator
- Gather rule details: direction, action, ports, protocols, and scopes. Use your change request or firewall policy analysis output.
- Estimate blast radius: count affected assets and subnets. Include dependent apps and users expected during the change window.
- Enter delivery readiness: testing coverage, logging, documentation, and rollback plan. Turn on redundancy if a failover path exists.
- Submit to generate impact scores and a risk band. For High or Critical, require stronger approvals and pre-checks.
- Export CSV for tracking and auditing, or download a PDF for change tickets. Re-run after scope reductions or test improvements to see score movement.
Scope and Exposure Drivers
Firewall rule changes shift risk by scope, direction, and action. In this calculator, exposure rises with more assets, subnets, ports, protocols, and traffic volume. Allow rules add a ten point uplift, while inbound direction adds seven points. A narrow change such as one subnet and one port can stay under thirty five, but broad multi subnet openings can exceed sixty quickly, escalating approvals and monitoring needs for audits and emergency change reviews.
Availability and Business Continuity
Availability impact is modeled from dependent applications and users, then adjusted for environment and readiness. Production adds fifteen points, staging adds eight, and development adds two. Criticality contributes up to twenty four points across levels one to five. Testing reduces the score at 0.2 points per percent, so moving from forty to eighty percent testing lowers availability by eight points. Missing redundancy adds ten points, raising outage concern for business hours cutovers.
Compliance and Audit Evidence
Compliance impact focuses on control touchpoints and audit evidence. Each impacted control adds ten points, reflecting segmentation, logging, or regulated zone boundaries that may need updated attestations. If logging is disabled, fifteen points are added, and incomplete documentation adds ten. Delete changes add ten more, because removing rules often requires proving compensating controls. A two control update with full evidence stays near twenty, while evidence gaps can routinely push beyond fifty five.
Operational Readiness and Rollback
Operational impact measures execution risk and rollback strength during the planned change window. Without a rollback plan, twenty points are added immediately. Recent incident rate adds fifteen points per level, so a rate of three contributes forty five points. Novelty is captured through similarity; below fifty percent similarity adds ten points, while fifty to seventy four adds five. Change type adds six for add, four for modify, and eight for delete actions.
Scoring Bands and Governance
The overall impact score is a weighted sum: thirty five percent exposure, thirty percent availability, twenty percent compliance, and fifteen percent operational. Scores map to four bands: low zero to thirty four, medium thirty five to fifty nine, high sixty to seventy nine, and critical eighty to one hundred. Confidence improves with testing, similarity, documentation, and logging. Use exports to track score movement after narrowing ports, raising tests, and adding rollback evidence.
FAQs
1) What does the impact score represent?
The impact score is a 0–100 estimate of change blast radius and execution risk, combining exposure, availability, compliance, and operational factors into one governance friendly number.
2) How should I interpret confidence?
Confidence reflects how well supported your inputs are. Higher testing, better similarity, logging, and documentation raise confidence, while missing rollback planning lowers it.
3) Why do allow rules score higher than deny rules?
Allow rules can expand reachable services and increase attack surface. The model adds an exposure uplift to reflect the additional verification usually required.
4) How can I lower a High or Critical result?
Reduce subnet and port scope, improve testing coverage, enable logging, complete documentation, and ensure a rollback plan. Recalculate to confirm the score drops into an acceptable band.
5) Can I use this for internal east west segmentation changes?
Yes. Select East‑West traffic direction and enter the affected assets, subnets, and dependent applications. Internal changes can still cause outages and lateral movement exposure.
6) What should I attach to a change ticket?
Download the PDF for a human readable summary and the CSV for audit tracking. Include assumptions, test evidence, and rollback steps aligned with the recommended approval path.