Exact duplicate
Action and every supported match field are equal. Confirm counters and references before removing either deployed entry.
Firewall Rule Conflict Checker
Describe ordered rules in a small vendor-neutral syntax. The checker compares protocol, source, destination, and service scope to find exact duplicates, conflicting decisions, and later rules that an earlier broader rule already matches.
Rules stay in the browser. Analysis follows the order entered and assumes first-match processing for this planning check.
Check an ordered vendor-neutral rule list
Use: action protocol source -> destination :port. IPv4 CIDRs and the word any are supported. One rule belongs on each line.
Example: allow tcp 10.0.0.0/8 -> 192.0.2.10/32 :443
Three findings require different corrections
A duplicate wastes review effort, a contradiction records competing decisions for the same scope, and a shadowed rule may never control traffic because an earlier broader rule already matches it.
Contradictory scope
The same protocol, source, destination, and service appear with different actions. In a first-match policy, order decides which action controls.
Shadowed later rule
An earlier rule covers all traffic described by the later entry. The later rule may be unreachable, redundant, or evidence that the earlier rule is too broad.
Why this cannot replace the firewall's native analyzer
Real products can use last-match evaluation, zones, interfaces, object groups, users, applications, schedules, NAT stages, state, implicit policy, and platform-specific optimization. This checker deliberately models only the visible ordered IPv4 fields. Treat a finding as a review question, then inspect the complete running policy and current vendor documentation.
Confirm the evaluation model first
Before acting on a shadow finding, verify whether the target policy uses first match, last match, or a vendor-specific compiled model. Also confirm where address translation occurs. The same visible entries can behave differently when NAT changes an address before or after the security rule evaluates it.
Turn each finding into a review question
| Finding | Question for the owner | Safe next step |
|---|---|---|
| Duplicate | Do both entries carry counters, comments, references, or dependencies? | Compare the running configuration before removing either entry. |
| Contradiction | Which action represents the approved requirement? | Confirm rule order and collect one allowed and one blocked example. |
| Shadowed rule | Is the earlier rule too broad, or is the later rule obsolete? | Narrow the approved scope and preserve a rollback. |
Translate any inverse-mask source with the wildcard mask calculator, then use the IP allowlist cleaner only when exact coverage and ownership are preserved.
Before removing a rule that appears unused, summarize a bounded event sample with the local firewall log analyzer and compare its counters with the same review window.
- Compare the simplified finding with zones, schedules, identities, applications, NAT, and implicit rules.
- Confirm which object definitions were active at the event time.
- Check whether another control permits or blocks the same path.
- Preserve the original configuration and a tested rollback.
Build the correction safely
Use the firewall rule planner to document the intended narrow path, owner, rollback, and expected tests. After implementation, apply the firewall testing method to one intended source and one source that must remain blocked.
Policy ordering and change control principles are covered in NIST SP 800-41 Rev. 1. No result from this page certifies a deployed ruleset.