Network segmentation (IT/OT separation) in SCADA systems - Step-by-Step Execution

Process Flow - Network segmentation (IT/OT separation)

Start: Network Traffic

↓

Traffic arrives at Firewall

↓

Check: Source = IT or OT?

↓

Route to IT Zone

↓

Apply IT Policies

↓

Allow or Block Traffic

↓

End

Network traffic is checked by a firewall to see if it comes from IT or OT. Then it is routed and controlled separately to keep systems safe.

Execution Sample

SCADA systems

firewall_rule = {
  'source_zone': 'IT',
  'destination_zone': 'OT',
  'action': 'block'
}
apply_firewall_rule(firewall_rule)

This code blocks traffic from the IT zone to the OT zone using a firewall rule.

Process Table

Step	Traffic Source	Traffic Destination	Firewall Check	Action Taken	Result
1	IT	OT	Source=IT, Dest=OT	Block	Traffic blocked between IT and OT
2	IT	IT	Source=IT, Dest=IT	Allow	Traffic allowed within IT zone
3	OT	OT	Source=OT, Dest=OT	Allow	Traffic allowed within OT zone
4	OT	IT	Source=OT, Dest=IT	Block	Traffic blocked between OT and IT
5	Unknown	IT	Source unknown	Block	Traffic blocked due to unknown source

💡 Traffic is either allowed or blocked based on source and destination zones to keep IT and OT separated.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5
traffic_source	None	IT	IT	OT	OT	Unknown
traffic_destination	None	OT	IT	OT	IT	IT
firewall_action	None	Block	Allow	Allow	Block	Block

Key Moments - 2 Insights

Why is traffic from IT to OT blocked but traffic within IT allowed?

Because the firewall rules separate IT and OT zones to protect OT systems. Execution table rows 1 and 2 show blocking between zones and allowing inside the same zone.

What happens if the source of traffic is unknown?

Traffic is blocked by default to keep the network safe, as shown in execution table row 5.

Visual Quiz - 3 Questions

Look at the execution table, what action is taken when traffic source is OT and destination is IT?

A Allow

B Log only

C Block

D Redirect

💡 Hint

Check row 4 in the execution table where source=OT and destination=IT.

At which step does the firewall allow traffic within the OT zone?

A Step 1

B Step 3

C Step 2

D Step 5

💡 Hint

Look at the execution table row where source and destination are both OT.

If the firewall action for unknown sources changed to 'Allow', how would the result in step 5 change?

A Traffic would be allowed

B Traffic would be blocked

C Traffic would be redirected

D No change

💡 Hint

Refer to variable_tracker and execution_table row 5 for current action and result.

Concept Snapshot

Network segmentation separates IT and OT zones.
Firewall checks source and destination zones.
Traffic between IT and OT is blocked.
Traffic inside the same zone is allowed.
Unknown sources are blocked by default.
This protects critical OT systems from IT threats.

Full Transcript

Network segmentation means dividing a network into parts to keep IT systems separate from OT systems. When network traffic arrives, a firewall checks if it comes from IT or OT. If traffic tries to go from IT to OT or OT to IT, the firewall blocks it. Traffic inside IT or inside OT is allowed. If the source is unknown, the firewall blocks the traffic to keep the network safe. This way, the OT systems that control important machines stay protected from IT network risks.

Practice

1. What is the main purpose of network segmentation between IT and OT systems in SCADA environments?

easy

A. To improve security by separating critical industrial systems from general IT networks

B. To increase the speed of data transfer between devices

C. To reduce the number of devices needed in the network

D. To allow all devices to communicate freely without restrictions

Solution

1. Step 1: Understand the role of network segmentation

   Network segmentation divides a network into parts to isolate sensitive systems from less secure ones.

2. Step 2: Apply this to IT and OT systems

   Separating IT (office systems) from OT (industrial control) protects critical SCADA systems from cyber threats.

3. Final Answer:

   To improve security by separating critical industrial systems from general IT networks -> Option A

4. Quick Check:

   Network segmentation = Security improvement [OK]

Hint: Segmentation means separation for security, not speed or device count [OK]

Common Mistakes:

• Thinking segmentation speeds up network
• Believing segmentation reduces devices
• Assuming segmentation allows free communication

2. Which of the following VLAN configurations correctly separates IT and OT traffic?

easy

A. VLAN 20 for IT devices, VLAN 10 for OT devices, but no traffic control

B. VLAN 10 for both IT and OT devices without any ACLs

C. VLAN 10 for IT devices, VLAN 20 for OT devices, with ACLs controlling traffic between them

D. No VLANs, all devices on the same network segment

Solution

1. Step 1: Identify VLAN usage for separation

   Using separate VLANs for IT and OT devices isolates their traffic logically.

2. Step 2: Check for access control lists (ACLs)

   ACLs control and restrict traffic between VLANs, enhancing security.

3. Final Answer:

   VLAN 10 for IT devices, VLAN 20 for OT devices, with ACLs controlling traffic between them -> Option C

4. Quick Check:

   Separate VLANs + ACLs = Proper segmentation [OK]

Hint: Separate VLANs plus ACLs control traffic properly [OK]

Common Mistakes:

• Using same VLAN for IT and OT
• Not applying ACLs between VLANs
• Ignoring VLANs and traffic control

3. Given this simplified network ACL rule:
permit ip 192.168.1.0 0.0.0.255 10.0.0.0 0.0.0.255
What does this rule allow?

medium

A. Allow all IP traffic from 192.168.1.x to 10.0.0.x

B. Block all traffic from 192.168.1.x to 10.0.0.x

C. Allow traffic only from 10.0.0.x to 192.168.1.x

D. Allow traffic from any IP to any IP

Solution

1. Step 1: Understand ACL syntax

   The rule permits IP traffic from source 192.168.1.0/24 to destination 10.0.0.0/24.

2. Step 2: Interpret the wildcard masks

   Wildcard 0.0.0.255 means any IP in the last octet, so 192.168.1.x to 10.0.0.x is allowed.

3. Final Answer:

   Allow all IP traffic from 192.168.1.x to 10.0.0.x -> Option A

4. Quick Check:

   permit ip source to destination = Allow traffic [OK]

Hint: permit ip source wildcard destination wildcard means allow that traffic [OK]

Common Mistakes:

• Confusing source and destination
• Misreading wildcard masks
• Assuming rule blocks traffic

4. You configured VLANs for IT and OT but OT devices cannot communicate with the SCADA server. What is the most likely cause?

medium

A. OT devices have incorrect IP addresses outside VLAN range

B. VLAN IDs for IT and OT are the same

C. SCADA server is powered off

D. Missing or incorrect ACL rules blocking OT to SCADA traffic

Solution

1. Step 1: Check VLAN separation

   If VLAN IDs are different, devices are separated logically, so VLAN ID conflict is unlikely.

2. Step 2: Review ACL rules

   ACLs often block traffic between VLANs; missing or wrong ACLs can prevent OT devices from reaching SCADA server.

3. Final Answer:

   Missing or incorrect ACL rules blocking OT to SCADA traffic -> Option D

4. Quick Check:

   ACL misconfiguration = communication failure [OK]

Hint: Check ACLs first when VLANs separate but no communication [OK]

Common Mistakes:

• Assuming VLAN IDs are same without checking
• Ignoring ACL impact on traffic
• Jumping to hardware power issues first

5. You want to allow only specific IT workstations to access OT SCADA devices. Which approach best achieves this while maintaining network segmentation?

hard

A. Place all IT and OT devices in the same VLAN to simplify access

B. Create a dedicated VLAN for those IT workstations and configure ACLs to allow only their IPs to OT VLAN

C. Disable all ACLs between IT and OT VLANs to allow free communication

D. Use a single firewall rule allowing all IT subnet to access OT subnet

Solution

1. Step 1: Understand segmentation with selective access

   Segmentation requires separate VLANs; selective access needs controlled rules.

2. Step 2: Apply VLAN and ACLs for fine control

   Creating a dedicated VLAN for allowed IT workstations and ACLs restricting access by IP ensures security and selective access.

3. Final Answer:

   Create a dedicated VLAN for those IT workstations and configure ACLs to allow only their IPs to OT VLAN -> Option B

4. Quick Check:

   Dedicated VLAN + ACLs = selective secure access [OK]

Hint: Use VLAN plus ACLs to limit access, not open networks [OK]

Common Mistakes:

• Mixing IT and OT in one VLAN
• Disabling ACLs completely
• Using broad firewall rules without IP filtering