The answer is TACACS+, because it is the AAA protocol designed to encrypt the entire authentication packet, including the username, password, and all other fields, using a shared secret key. This full packet encryption is a critical technical differentiator from RADIUS, which only encrypts the password field while leaving the rest of the packet in cleartext. On the CompTIA Network+ N10-009 exam, this distinction is frequently tested in questions about secure network device authentication, often presenting RADIUS as a common trap answer. The exam expects you to know that TACACS+ separates authentication, authorization, and accounting processes, and that its complete packet encryption makes it the preferred choice for environments requiring maximum security for AAA transactions. To remember this, think of TACACS+ as “Total Authentication Coverage” because it encrypts everything, while RADIUS only “Radiates” protection to the password.
N10-009 Network Security Practice Question
This N10-009 practice question tests your understanding of network security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A network security administrator is configuring authentication for network devices and wants to use a protocol that supports separate encryption of the entire authentication packet. Which of the following protocols is designed to encrypt the entire authentication packet and is commonly used with AAA services?
Why wrong: RADIUS encrypts only the password field in an authentication packet; other fields like the username are sent in cleartext.
B
TACACS+
TACACS+ encrypts the entire payload of the authentication packet, providing greater confidentiality for all authentication information.
C
LDAP
Why wrong: LDAP is a directory access protocol; while it can be used for authentication, it does not inherently encrypt the entire packet unless used over TLS.
D
Kerberos
Why wrong: Kerberos uses symmetric key cryptography and tickets but does not encrypt the entire authentication packet; it relies on a different mechanism.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
TACACS+
TACACS+ is the correct answer because it encrypts the entire authentication packet, including the username, password, and all other fields, using a shared secret key. This full-packet encryption is a key differentiator from RADIUS, which only encrypts the password field. TACACS+ is commonly used with AAA services to provide separate authentication, authorization, and accounting processes.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
RADIUS
Why it's wrong here
RADIUS encrypts only the password field in an authentication packet; other fields like the username are sent in cleartext.
✓
TACACS+
Why this is correct
TACACS+ encrypts the entire payload of the authentication packet, providing greater confidentiality for all authentication information.
Related concept
Read the scenario before looking for a memorised answer.
✗
LDAP
Why it's wrong here
LDAP is a directory access protocol; while it can be used for authentication, it does not inherently encrypt the entire packet unless used over TLS.
✗
Kerberos
Why it's wrong here
Kerberos uses symmetric key cryptography and tickets but does not encrypt the entire authentication packet; it relies on a different mechanism.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that RADIUS encrypts the entire packet because it uses a shared secret, but in reality, only the password is encrypted, whereas TACACS+ encrypts the full payload.
Detailed technical explanation
How to think about this question
TACACS+ uses TCP port 49 and separates the three A's (Authentication, Authorization, Accounting) into distinct packets, allowing granular control. The entire TACACS+ packet body is encrypted using a shared secret and MD5-based hash, while the header remains in cleartext for routing. In contrast, RADIUS uses UDP and only encrypts the password attribute (User-Password) using a shared secret and MD5, leaving other attributes exposed.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A junior network technician can log in to a core router but cannot reach the enable prompt or configuration mode. The AAA server is authenticating the login — but the authorisation policy only grants privilege level 1, not 15. Authentication (who you are) is working; authorisation (what you can do) is not.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 question in full detail.
Network Security — This question tests Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: TACACS+ — TACACS+ is the correct answer because it encrypts the entire authentication packet, including the username, password, and all other fields, using a shared secret key. This full-packet encryption is a key differentiator from RADIUS, which only encrypts the password field. TACACS+ is commonly used with AAA services to provide separate authentication, authorization, and accounting processes.
What should I do if I get this N10-009 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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