Firewall and DMZ for SCADA in SCADA systems - Step-by-Step Execution

Process Flow - Firewall and DMZ for SCADA

External Network

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Firewall: Block/Allow Rules

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DMZ Zone: Isolated Network

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SCADA Network: Protected Systems

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Internal SCADA Devices & Controllers

Data flows from outside through the firewall, which filters traffic, then enters the DMZ, an isolated zone, before reaching the protected SCADA network.

Execution Sample

SCADA systems

firewall-cmd --zone=dmz --add-source=192.168.1.0/24
firewall-cmd --zone=dmz --add-port=502/tcp
firewall-cmd --zone=dmz --add-rich-rule='rule family=ipv4 source address=10.0.0.5 accept'
firewall-cmd --zone=public --remove-source=192.168.1.0/24

Commands to configure firewall zones and rules to isolate SCADA traffic in the DMZ.

Process Table

Step	Command	Action	Result	System State
1	firewall-cmd --zone=dmz --add-source=192.168.1.0/24	Add source network to DMZ zone	Success	DMZ zone includes 192.168.1.0/24
2	firewall-cmd --zone=dmz --add-port=502/tcp	Allow Modbus TCP port in DMZ	Success	Port 502/tcp open in DMZ
3	firewall-cmd --zone=dmz --add-rich-rule='rule family=ipv4 source address=10.0.0.5 accept'	Allow specific SCADA device IP	Success	10.0.0.5 allowed in DMZ
4	firewall-cmd --zone=public --remove-source=192.168.1.0/24	Remove source from public zone	Success	192.168.1.0/24 removed from public zone
5	Traffic from 192.168.1.10 to port 502	Check firewall rules	Allowed	Traffic passes through DMZ to SCADA
6	Traffic from 10.0.0.6 to port 502	Check firewall rules	Blocked	Traffic blocked by firewall
7	Traffic from external network to SCADA	Check firewall rules	Blocked	External traffic blocked unless allowed
8	End	No more commands	N/A	Firewall and DMZ configured correctly

💡 All firewall rules applied; traffic filtered according to DMZ and SCADA protection policies.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
DMZ Sources	[]	[192.168.1.0/24]	[192.168.1.0/24]	[192.168.1.0/24]	[192.168.1.0/24]	[192.168.1.0/24]
DMZ Open Ports	[]	[]	[502/tcp]	[502/tcp]	[502/tcp]	[502/tcp]
DMZ Allowed IPs	[]	[]	[]	[10.0.0.5]	[10.0.0.5]	[10.0.0.5]
Public Sources	[192.168.1.0/24]	[192.168.1.0/24]	[192.168.1.0/24]	[192.168.1.0/24]	[]	[]

Key Moments - 3 Insights

Why do we remove the source network from the public zone after adding it to the DMZ?

Because a source network can only belong to one zone at a time. Removing it from public ensures traffic is filtered by DMZ rules, as shown in step 4 of the execution_table.

Why is traffic from 10.0.0.6 blocked even though port 502 is open in the DMZ?

Because only the IP 10.0.0.5 is explicitly allowed by the rich rule in step 3. Other IPs like 10.0.0.6 are blocked, as seen in step 6.

What is the purpose of the DMZ in SCADA network security?

The DMZ isolates SCADA systems from external networks, filtering traffic through firewall rules before it reaches sensitive devices, as shown in the concept_flow and execution_table steps.

Visual Quiz - 3 Questions

Look at the execution_table at step 3. Which IP address is allowed explicitly in the DMZ?

A 192.168.1.10

B 10.0.0.5

C 10.0.0.6

D 192.168.1.0/24

💡 Hint

Check the 'Command' and 'Result' columns at step 3 in the execution_table.

At which step does the source network 192.168.1.0/24 get removed from the public zone?

A Step 1

B Step 2

C Step 4

D Step 5

💡 Hint

Look for the command that removes the source from the public zone in the execution_table.

If we add 10.0.0.6 to the allowed IPs in the DMZ, what will happen to traffic from 10.0.0.6 at step 6?

A It will be allowed

B It will still be blocked

C It will be redirected

D It will cause an error

💡 Hint

Refer to the variable_tracker for DMZ Allowed IPs and the execution_table step 6.

Concept Snapshot

Firewall and DMZ for SCADA:
- Firewall filters traffic between external and SCADA networks.
- DMZ is an isolated zone for controlled access.
- Add source IPs and ports to DMZ zone.
- Remove sources from public zone to avoid conflicts.
- Only allowed IPs can access SCADA services through DMZ.

Full Transcript

This visual execution shows how a firewall and DMZ protect SCADA systems. Traffic from external networks first hits the firewall, which filters it based on rules. The DMZ acts as a buffer zone isolating SCADA devices. Commands add source IP ranges and ports to the DMZ zone and remove them from the public zone to avoid overlap. Specific SCADA device IPs are allowed explicitly. Traffic tests show allowed and blocked connections based on these rules. Variables track the state of sources, ports, and allowed IPs in each zone. Key moments clarify why sources must be removed from public when added to DMZ, why only allowed IPs pass, and the DMZ's role in security. Quizzes test understanding of IP allowances, zone changes, and traffic outcomes. This step-by-step trace helps beginners see how firewall and DMZ configurations protect SCADA networks.