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Firewall Rule Complexity Calculator

Work out firewall rule complexity instantly with clear inputs, formula shown and shareable results.

About Firewall Rule Complexity Calculator

Firewall policies decay: rules are added for projects and never removed, so shadowed rules accumulate behind broader ones and any-any entries survive from long-forgotten troubleshooting. The hygiene score penalises both, and the evaluation count shows why complexity also costs performance — every rule and object multiplies the worst-case match work per new flow.

Formula

Policy complexity

evaluations = rules x objects per rule; hygiene = 100 - shadowed% - 10 x any-any%, floored at 0

Worked example

With the default values below, Firewall Rule Complexity Calculator returns Policy hygiene score (0-100) of 57.2. Change any input above and every figure here is recalculated in your browser.

Inputs used

Rules in the policyminimum 1
1,800
Average objects per ruleminimum 1
6
Shadowed or unused rulesminimum 0
320
Rules with any-any elementsminimum 0
45

Results

Policy hygiene score (0-100)
57.2
Worst-case match evaluations per packet
10,800
Rules that never match
17.8%
Rules containing any-any elements
2.5%

Step by step

  1. 1Values used
  2. 2Policy complexity
  3. 3Policy hygiene score (0-100)= 57.2
  4. 4Worst-case match evaluations per packet= 10,800
  5. 5Rules that never match= 17.8
  6. 6Rules containing any-any elements= 2.5

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why are shadowed rules dangerous rather than merely untidy?

They hide intent. An administrator editing a rule that never matches believes they have changed behaviour when they have not, and cleanup later can suddenly open or close unexpected paths.

How often should policies be reviewed?

PCI DSS requires at least every six months. Automated analysis tools that flag shadowing, redundancy and unused rules make it practical to do continuously.

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