- A
HMAC-SHA-96
Why wrong: HMAC-SHA-96 is used when SHA is configured, not MD5.
- B
HMAC-MD5-96
RFC 3414 defines HMAC-MD5-96 as the authentication protocol for usmHMACMD5AuthProtocol.
- C
HMAC-SHA-256
Why wrong: HMAC-SHA-256 is not a standard SNMPv3 authentication protocol; only MD5 and SHA (96-bit) are defined in the base RFC.
- D
No HMAC is used; MD5 is used directly.
Why wrong: SNMPv3 always uses HMAC for authentication, not raw MD5.
Question 139 of 2,152
HMAC-MD5-96: Default Authentication Algorithm for SNMPv3
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.
When troubleshooting SNMPv3 authentication failures, which default HMAC algorithm is used if the user is configured with "auth md5"?
Quick Answer
The answer is HMAC-MD5-96. When a user is configured with "auth md5" in SNMPv3, the protocol defaults to the HMAC-MD5-96 algorithm for authentication, which produces a 96-bit message digest to verify message integrity and origin. This is defined in RFC 3414 and is the standard behavior because MD5 was the original hash specified for SNMPv3's User-based Security Model (USM). On the Cisco CCNP ENARSI 300-410 exam, this often appears in troubleshooting scenarios where authentication failures occur due to mismatched algorithms—a common trap is assuming "auth md5" uses full MD5 rather than the truncated HMAC variant. Remember that SNMPv3 always truncates the hash to 96 bits for both MD5 and SHA, so the "96" in the algorithm name is the key detail. A useful memory tip: think of "MD5-96" as "MD5 minus 32 bits," since MD5 normally produces 128 bits, but SNMPv3 clips it down to 96 for efficiency.
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
✓
HMAC-MD5-96
When a user is configured with 'auth md5' in SNMPv3, the default HMAC algorithm used is HMAC-MD5-96. This is defined in RFC 3414, which specifies that the authentication protocol 'MD5' actually refers to HMAC-MD5-96, not raw MD5. The HMAC construction provides keyed hashing for message integrity and authentication, and the '-96' indicates that the output is truncated to 96 bits (12 bytes).
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.
- ✗
HMAC-SHA-96
Why it's wrong here
HMAC-SHA-96 is used when SHA is configured, not MD5.
- ✓
HMAC-MD5-96
Why this is correct
RFC 3414 defines HMAC-MD5-96 as the authentication protocol for usmHMACMD5AuthProtocol.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
HMAC-SHA-256
Why it's wrong here
HMAC-SHA-256 is not a standard SNMPv3 authentication protocol; only MD5 and SHA (96-bit) are defined in the base RFC.
- ✗
No HMAC is used; MD5 is used directly.
Why it's wrong here
SNMPv3 always uses HMAC for authentication, not raw MD5.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that 'auth md5' uses raw MD5 directly, when in fact SNMPv3 always wraps the hash in an HMAC construction, and the '-96' suffix indicates the truncated output length.
Detailed technical explanation
How to think about this question
Under the hood, HMAC-MD5-96 applies the MD5 hash function twice with a key to produce a 128-bit digest, which is then truncated to 96 bits for the final message authentication code. This truncation reduces the output size to fit within the SNMP message format while still providing strong integrity protection. In real-world troubleshooting, a common issue is that the SNMP engine IDs must match between the manager and agent for the authentication key derivation to succeed, even if the HMAC algorithm is correctly configured.
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.
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: HMAC-MD5-96 — When a user is configured with 'auth md5' in SNMPv3, the default HMAC algorithm used is HMAC-MD5-96. This is defined in RFC 3414, which specifies that the authentication protocol 'MD5' actually refers to HMAC-MD5-96, not raw MD5. The HMAC construction provides keyed hashing for message integrity and authentication, and the '-96' indicates that the output is truncated to 96 bits (12 bytes).
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.
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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