- A
The NMS is still configured with the old credentials that do not include the privacy protocol and key.
SNMPv3 requires that both the agent and NMS agree on the security level; if the agent requires privacy but the NMS does not provide it, the request fails.
- B
The router's SNMP engine ID changed when the user was modified.
Why wrong: Modifying a user does not change the engine ID.
- C
The privacy protocol (e.g., AES) is not supported on the router.
Why wrong: If the protocol were unsupported, the configuration command would be rejected.
- D
The NMS must restart to recognize the new security level.
Why wrong: SNMPv3 credentials are typically updated dynamically on the NMS.
Question 157 of 2,152
Why Adding Privacy to SNMPv3 User Breaks NMS Polling
This 300-410 practice question tests your understanding of snmp troubleshooting. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 engineer configures SNMPv3 with authentication only (no privacy) on a router. The NMS can poll the router successfully. Later, the engineer adds the 'priv' option to the user configuration. The NMS now fails to poll the router. Which is the most likely explanation?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Quick Answer
The answer is that the NMS is still configured with the old credentials that do not include the privacy protocol and key. When you add the priv option to an SNMPv3 user configuration on the router, the device now expects both authentication and encryption for every response. The NMS, still using the original authentication-only credentials, can authenticate the request, but when it receives the encrypted response, it lacks the correct privacy key to decrypt it, causing the NMS to discard the packet and report a polling failure. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of SNMPv3 security level consistency—specifically that the securityLevel on both the agent and manager must match exactly. A common trap is assuming authentication alone will still work after privacy is enabled, or that the NMS will automatically detect the change. Memory tip: think "add priv, update NMS"—if you change the lock, you must give everyone the new key.
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 NMS is still configured with the old credentials that do not include the privacy protocol and key.
When the engineer adds the 'priv' option to the SNMPv3 user configuration on the router, the security level changes from authNoPriv to authPriv. The NMS must be updated with the matching privacy protocol (e.g., AES or DES) and the corresponding privacy key. If the NMS still uses the old credentials without the privacy parameters, the authentication will succeed but the privacy decryption will fail, causing the NMS to reject the response and report a polling failure.
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.
- ✓
The NMS is still configured with the old credentials that do not include the privacy protocol and key.
Why this is correct
SNMPv3 requires that both the agent and NMS agree on the security level; if the agent requires privacy but the NMS does not provide it, the request fails.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The router's SNMP engine ID changed when the user was modified.
Why it's wrong here
Modifying a user does not change the engine ID.
- ✗
The privacy protocol (e.g., AES) is not supported on the router.
Why it's wrong here
If the protocol were unsupported, the configuration command would be rejected.
- ✗
The NMS must restart to recognize the new security level.
Why it's wrong here
SNMPv3 credentials are typically updated dynamically on the NMS.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that changing an SNMPv3 user's security level only requires a change on the router, but the trap is that the NMS must also be updated with the matching privacy protocol and key, otherwise the mismatch in security levels causes the polling to fail.
Trap categories for this question
Command / output trap
If the protocol were unsupported, the configuration command would be rejected.
Detailed technical explanation
How to think about this question
SNMPv3 uses a User-based Security Model (USM) where each user has a security level (noAuthNoPriv, authNoPriv, or authPriv). When privacy is enabled, the NMS must know the exact privacy protocol (e.g., CFB128-AES-128 per RFC 3826) and the privacy key, which is derived from the user's passphrase using a key localization algorithm tied to the engine ID. If the NMS sends a GetRequest with authNoPriv but the router expects authPriv, the router will encrypt the response, and the NMS will fail to decrypt it, leading to a timeout or authentication error.
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 practitioner preparing for the 300-410 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Quick reference
Symmetric Encryption Algorithm Comparison
| Algorithm | Key Size | Block Size | Status | Notes |
|---|---|---|---|---|
| AES-128 | 128-bit | 128-bit | Current standard | NIST approved; WPA3, TLS |
| AES-256 | 256-bit | 128-bit | Current standard | Preferred for sensitive / govt data |
| 3DES | 112-bit effective | 64-bit | Deprecated (2023) | Replaced by AES |
| DES | 56-bit | 64-bit | Broken | Cracked in < 24 h; never deploy |
| ChaCha20 | 256-bit | Stream cipher | Current | TLS 1.3, WireGuard |
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 300-410 question test?
SNMP Troubleshooting — This question tests SNMP Troubleshooting — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The NMS is still configured with the old credentials that do not include the privacy protocol and key. — When the engineer adds the 'priv' option to the SNMPv3 user configuration on the router, the security level changes from authNoPriv to authPriv. The NMS must be updated with the matching privacy protocol (e.g., AES or DES) and the corresponding privacy key. If the NMS still uses the old credentials without the privacy parameters, the authentication will succeed but the privacy decryption will fail, causing the NMS to reject the response and report a polling failure.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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