CND Practice Question: Network Security Controls Protocols And Devices
A security engineer is configuring a stateful inspection firewall and needs to handle incoming traffic for an active FTP data connection operating in passive mode. What specific challenge does passive FTP present to the firewall, and how does the firewall resolve it?
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
✓
The server initiates a connection back to a random client port, which is blocked unless an Application Layer Gateway (ALG) dynamically opens the port.
In passive FTP, the client initiates both the control and data connections, but the server dictates the dynamic high-port number for the data channel. Stateful firewalls use an application layer gateway (ALG) inspect the FTP control channel negotiation to dynamically open the required high-port for the data connection.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The firewall must permanently open all ports above 1024 to allow inbound FTP file transfers.
Why it's wrong here
Permanently opening all high ports creates a massive security risk; firewalls use dynamic pinholing via ALGs instead.
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Passive FTP encrypts the control channel by default, preventing the firewall from inspecting port numbers.
Why it's wrong here
Standard FTP control and data channels are unencrypted unless explicit or implicit FTPS is used.
- ✗
The client uses UDP port 69, which requires disabling stateful inspection for TFTP traffic.
Why it's wrong here
TFTP uses UDP port 69, but FTP uses TCP ports 21 and dynamic ports, not TFTP.
- ✓
The server initiates a connection back to a random client port, which is blocked unless an Application Layer Gateway (ALG) dynamically opens the port.
Why this is correct
Passive FTP requires an FTP ALG on the firewall to inspect control commands and dynamically permit the server-specified data port.
Visual reference
About these practice questions
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed August 2026 · checked against the official EC-Council exam blueprint
This CND practice question is part of Courseiva's free EC-Council certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CND exam.