DMZ Rule Planner Calculator

Planner Inputs

Example Data Table

Formula Used

The calculator converts environment inputs into a net risk score (0–100) using weighted exposure factors and control reductions:

• Exposure factors: services count, port count, sensitivity, data class, admin model, segmentation, egress openness, change rate, and third-party paths.
• Control reductions: MFA, TLS, WAF, IDS/IPS, logging depth, and patch cadence.

NetRisk = clamp(Exposure − Controls, 0, 100) and Score = 100 − NetRisk. Higher scores represent stronger rule posture.

How to Use This Calculator

1. Enter your DMZ size, exposed ports, sensitivity, and data class.
2. Choose your admin path, segmentation, and egress posture.
3. Set control coverage: MFA, TLS, WAF, IDS, logging, and patch cadence.
4. Add custom flows that your applications require, with clear justification.
5. Click Calculate Plan to get a score, recommendations, and a rule table.
6. Download CSV for tickets or PDF for approvals and audits.

Exposure Surface Metrics

This planner treats every internet-facing service as an exposure unit. Three public services and eighteen open ports is a common mid-size DMZ baseline. As services grow beyond five, operational drift usually appears: duplicated listeners, temporary ports, and “just in case” rules. Keeping a documented allowlist lets you prove why a port exists and who owns it during reviews.

Control Coverage and Score Impact

Controls reduce risk only when they are enforced consistently. MFA and a bastion path reduce privileged reachability, while TLS and a gateway reduce opportunistic interception and application abuse. Enhanced logging adds change visibility and supports incident reconstruction. Faster patch cadence matters most in DMZ tiers because exploitation windows are shorter for exposed hosts. A patch cycle of thirty days or less typically improves the score by several points compared with ninety days.

Segmentation and East-West Flows

A strict zone model separates web, application, admin, and internal data tiers. This tool always suggests an explicit web-to-app allowlist and an app-to-data allowlist. If segmentation is partial or flat, rule intent becomes unclear and lateral movement becomes easier. Clear direction labels help change boards understand whether a flow is north-south or east-west. Use unique subnet ranges per tier and restrict admin protocols to the admin zone only.

Egress Discipline and Required Exceptions

Outbound access is frequently the hidden risk in DMZ designs. Default-deny egress blocks malware callbacks and data staging, but still permits required services through explicit exceptions. DNS and NTP are typical: route them to approved resolvers and time sources, then log usage. When egress is temporarily open, attach an expiry date and monitor destinations. Prefer HTTPS proxying for update repositories and vendor APIs.

Operational Readiness and Audit Artifacts

A plan is usable only when it is repeatable. Exporting CSV supports ticketing and peer review, while a PDF snapshot supports approvals and evidence. Track rule justifications, logging level, and owner contacts. Review quarterly at minimum, and after major application changes. A consistent template reduces change risk and speeds troubleshooting. Scores of eighty or higher indicate low exposure, while sixty-five to seventy-nine suggests targeted hardening. Document rejected rule requests to prevent rework and to show governance maturity.

FAQs

1) What does the score represent?

The score is 100 minus a weighted net-risk value. More exposed services, ports, and weak pathways lower it, while MFA, TLS, strong logging, segmentation, and faster patching raise it.

2) Can I use this output as firewall policy directly?

Use it as a planning template, not as a final rule push. Validate addresses, ports, owners, and change approvals in your environment before implementation.

3) Why is egress restriction emphasized?

Outbound rules are often overlooked. Default-deny egress reduces command-and-control callbacks and data exfiltration paths, while exceptions remain explicit and auditable.

4) How should I define “custom services”?

List only business-required listeners, ideally as protocol/port pairs like TCP/8443. Avoid broad ranges. Tie each item to an owner, ticket, and monitoring plan.

5) What logging level should I choose?

Enhanced logging is recommended for DMZ rules because it captures flow visibility and admin changes. Basic logging may miss critical context during investigations and audits.

6) How often should rules be reviewed?

Review quarterly at minimum, and after major application or infrastructure changes. Also review after incidents, control gaps, or repeated temporary exceptions.