Lion Cipher Lab
Find unused firewall rules from hit counters and retire them safely
- Cyber / Security Engineer
- Intermediate
- ~40 min
- Free · no account required
Why it matters
Firewall rule bases collect rules nobody remembers adding. A project ends but its access rule stays. A temporary rule for a migration becomes permanent. A partner relationship ends and their network is still allowed in. Each rule that is no longer needed is attack surface: a path an attacker can use that nobody is watching. NIST's firewall guidance (SP 800-41) treats reviewing and cleaning up rulesets as part of firewall management. The hard question is which rules are safe to remove. The usual evidence is hit counters. iptables counts packets and bytes for every rule, and iptables-save -c…
What you'll learn
- iptables packet and byte counters
- measuring rule usage over a window with two snapshots
- why one snapshot cannot show recent usage
- documenting rarely used rules so they are not retired by mistake
- detecting counter resets that invalidate the window
- retiring rules safely: disable, watch, then delete
- the difference between unused and unnecessary
Steps in this lab
- Counters, and why one snapshot is not enough
- The two snapshots
- Write the usage analyzer
- Run it, and compare with a single snapshot
- Test the reset guard
- Retire rules safely: ask, disable, watch, delete