OT security lab · Level 3 of 8
Firewall rules: the minimum, then deny by default
Level 3 of 8 in the OT security lab: a free OT security exercise at Intermediate level. Write the fewest allow-rules that keep production running between the levels, remove the old open rules and deny everything else.
Free · no download. Your work is saved on this device. Updated 18 Oct 2026.
The brief
- Client
- Halden Dairy Co-operative
- Site
- Dairy plant firewalls, Halden
- Work order
- WO-OTS-103
- Task code
- OTS-03
- Difficulty
- Intermediate
- Type of work
- Configuration
Write the fewest allow-rules that keep production running between the levels, remove the old open rules and deny everything else.
Skills you practise
- Firewall rule order
- Least privilege
- Deny by default
- Over-broad rules
What the test checks
The acceptance test marks the skills this level practises.
- Firewall rule order
- Least privilege
- Deny by default
- Over-broad rules
In this lab
- Purdue levels, zones and conduits
- Firewall rules, remote access and logs
- Patch plans, backups and an incident drill
Levels in the OT security lab
Previous: Zones and conduits: split a flat networkNext: Remote access: the vendor comes in through the DMZ
- Map the plant network: put every device on its level
- Zones and conduits: split a flat network
- Firewall rules: the minimum, then deny by default
- Remote access: the vendor comes in through the DMZ
- Spot the intruder: the events that matter in a day's log
- Patch or protect: choose within the maintenance window
- Backup and recovery: known-good copies and a proved restore
- Incident drill: a simulated note on an operator screen
Part of the OT security lab
Map a plant network, split it into zones, write the firewall rules, read the logs and run the response drill.
Feeds these internships: SCADA and HMI.