mediumMultiple Choice
ISC2 CC Practice Question: Refer to the exhibit
Network Topology
Refer to the exhibit. An administrator notices that external access to the MySQL database (port 3306) is blocked, but internal access should be allowed. What change should be made?
⚠ Common exam trap
ISC2 often tests the distinction between INPUT and FORWARD chains, and the trap here is that candidates mistakenly think adding a rule to the FORWARD chain will fix the issue, not realizing that traffic to the local MySQL service is processed by the INPUT chain.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a rule to allow traffic from internal IP range to port 3306
The exhibit shows a DROP rule for port 3306 in the INPUT chain, which blocks all incoming traffic to the MySQL database. To allow internal access while keeping external access blocked, a specific rule must be added to ACCEPT traffic from the internal IP range to port 3306, placed before the DROP rule. This ensures that internal packets are matched first and permitted, while external packets hit the DROP rule and are rejected. Simply modifying or removing the DROP rule would allow all traffic, violating the requirement to block external access.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Change the DROP rule to ACCEPT for port 3306
Why it's wrong here
Changing the DROP to ACCEPT for port 3306 would expose MySQL to external networks, which the requirement forbids; the rule must remain restrictive for external traffic. ACCEPT on that rule is correct only where unrestricted access from any source is genuinely intended.
- ✗
Allow port 3306 in the FORWARD chain
Why it's wrong here
The FORWARD chain governs traffic routed through the host, not traffic destined to the host itself, so a rule there never matches inbound MySQL connections. FORWARD rules are correct when filtering packets traversing the system, such as between network segments.
- ✓
Create a rule to allow traffic from internal IP range to port 3306
Why this is correct
Allowing the internal IP range inbound to TCP 3306 satisfies the stem's constraint that internal access should be permitted while external access stays blocked. A network security group rule scoped to the internal subnet permits only that source, leaving the existing deny for external traffic intact.
- ✗
Remove the DROP rule for port 3306
Why it's wrong here
Deleting the DROP rule removes all filtering of port 3306, permitting external connections the scenario explicitly prohibits. Removing a rule is correct only when the traffic it blocks should be entirely unrestricted, not when internal-only access is required.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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