The answer is that pings across the VPN fail and the output of show crypto isakmp sa displays no SA, specifically showing MM_NO_STATE. This indicates a failure in IKE Phase 1 negotiation, where mismatched IKE parameters—such as encryption algorithm, hash method, Diffie-Hellman group, or authentication pre-shared key—prevent the peers from agreeing on a common transform set, thus blocking the ISAKMP security association from forming. On the Cisco CCNP ENARSI 300-410 exam, this symptom tests your ability to distinguish Phase 1 failures from Phase 2 or routing issues; a common trap is assuming a ping failure alone points to a routing problem, but the absence of any ISAKMP SA with MM_NO_STATE specifically isolates the mismatch to IKE parameters. For a quick memory tip, remember “No State, No Match”—if you see MM_NO_STATE in the SA output, the IKE parameters are mismatched.
300-410 IPsec Site-to-Site VPN Practice Question
This 300-410 practice question tests your understanding of ipsec site-to-site vpn. 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.
Which THREE symptoms indicate a potential IPsec site-to-site VPN failure due to mismatched IKE parameters? (Choose THREE.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The 'show crypto isakmp sa' output shows 'MM_NO_STATE'.
Option A is correct because the 'show crypto isakmp sa' output showing 'MM_NO_STATE' indicates that the IKE Phase 1 negotiation has failed to progress past the Main Mode initial exchange. This typically occurs when IKE parameters such as encryption, hash, Diffie-Hellman group, or authentication method do not match between the two VPN peers, preventing the establishment of an ISAKMP security association.
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 'show crypto isakmp sa' output shows 'MM_NO_STATE'.
Why this is correct
MM_NO_STATE indicates that IKE phase 1 has not completed, often due to mismatched parameters.
Related concept
Read the scenario before looking for a memorised answer.
✗
The 'show crypto ipsec sa' output shows packet errors.
Why it's wrong here
Packet errors in IPsec SA can indicate many issues, not specifically IKE mismatches.
✓
The router logs display '%CRYPTO-4-IKMP_NO_POLICY' error messages.
Why this is correct
This error indicates that no matching IKE policy was found, often due to mismatched parameters.
Related concept
Read the scenario before looking for a memorised answer.
✗
The 'show crypto isakmp sa' output shows 'ACTIVE' state.
Why it's wrong here
ACTIVE state means phase 1 is successful, so no mismatch.
✓
Pings across the VPN fail, and 'show crypto isakmp sa' shows no SA.
Why this is correct
No ISAKMP SA indicates phase 1 failure, often due to mismatched IKE parameters.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between IKE Phase 1 and Phase 2 failure symptoms, and the trap here is confusing packet errors in 'show crypto ipsec sa' (Phase 2) with IKE parameter mismatches (Phase 1), leading candidates to incorrectly select option B.
Detailed technical explanation
How to think about this question
IKE Phase 1 uses Main Mode (6 messages) or Aggressive Mode (3 messages) to negotiate parameters and establish a secure channel. The 'MM_NO_STATE' state in the ISAKMP SA table means the negotiation is stuck at the first or second message pair, often due to a mismatch in the IKE policy set (e.g., encryption algorithm, hash algorithm, or Diffie-Hellman group). In real-world scenarios, this can also be caused by a firewall blocking UDP port 500 or 4500, or by a mismatch in the pre-shared key.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
IPsec Site-to-Site VPN — This question tests IPsec Site-to-Site VPN — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The 'show crypto isakmp sa' output shows 'MM_NO_STATE'. — Option A is correct because the 'show crypto isakmp sa' output showing 'MM_NO_STATE' indicates that the IKE Phase 1 negotiation has failed to progress past the Main Mode initial exchange. This typically occurs when IKE parameters such as encryption, hash, Diffie-Hellman group, or authentication method do not match between the two VPN peers, preventing the establishment of an ISAKMP security association.
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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Question Discussion
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