The answer is an IKE mode mismatch, specifically that the initiator is using aggressive mode while the responder expects main mode. MM_NO_STATE in the output of show crypto isakmp sa indicates that IKE Phase 1 has not yet established any security association, and this particular state often arises when the responder receives an unexpected first packet format. In aggressive mode, the initiator bundles all parameters—including the preshared key identity—into a single packet, but if the responder is configured for main mode, it will not recognize this exchange and will drop the packet before any state is created. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of IKE negotiation flows and the subtle differences between main and aggressive mode; a common trap is assuming a policy mismatch or firewall issue when the real culprit is the mode itself. Remember the mnemonic: “MM_NO_STATE means the mode is misaligned—aggressive sent, main expected.”
300-410 Route Summarization Practice Question
This 300-410 practice question tests your understanding of route summarization. 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.
An engineer configures IPsec between two routers. The tunnel does not come up. 'show crypto isakmp sa' shows MM_NO_STATE. 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.
The IKE mode is mismatched: the initiator is using aggressive mode, but the responder expects main mode.
Aggressive mode and main mode are incompatible. If one side uses aggressive mode and the other uses main mode, the IKE exchange will fail, resulting in MM_NO_STATE.
B
The pre-shared key is mismatched.
Why wrong: A mismatched pre-shared key would typically result in MM_KEY_EXCH or MM_AUTH state, not MM_NO_STATE.
C
The transform-set is mismatched.
Why wrong: Transform-set mismatch would be detected during Phase 2, not Phase 1, so the state would be MM_ACTIVE for Phase 1.
D
The access-list for interesting traffic is misconfigured.
Why wrong: Interesting traffic only triggers IPsec; it does not affect IKE Phase 1 state.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The IKE mode is mismatched: the initiator is using aggressive mode, but the responder expects main mode.
MM_NO_STATE indicates that IKE Phase 1 has not started. In aggressive mode, the initiator sends all IKE parameters in the first packet, and if the responder does not have a matching policy, the exchange fails. However, a common edge case is that the responder is configured for main mode while the initiator is configured for aggressive mode, causing the exchange to fail before any state is established.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 IKE mode is mismatched: the initiator is using aggressive mode, but the responder expects main mode.
Why this is correct
Aggressive mode and main mode are incompatible. If one side uses aggressive mode and the other uses main mode, the IKE exchange will fail, resulting in MM_NO_STATE.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The pre-shared key is mismatched.
Why it's wrong here
A mismatched pre-shared key would typically result in MM_KEY_EXCH or MM_AUTH state, not MM_NO_STATE.
✗
The transform-set is mismatched.
Why it's wrong here
Transform-set mismatch would be detected during Phase 2, not Phase 1, so the state would be MM_ACTIVE for Phase 1.
✗
The access-list for interesting traffic is misconfigured.
Why it's wrong here
Interesting traffic only triggers IPsec; it does not affect IKE Phase 1 state.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 300-410 NAT questions on configuration and troubleshooting.
Route Summarization — This question tests Route Summarization — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The IKE mode is mismatched: the initiator is using aggressive mode, but the responder expects main mode. — MM_NO_STATE indicates that IKE Phase 1 has not started. In aggressive mode, the initiator sends all IKE parameters in the first packet, and if the responder does not have a matching policy, the exchange fails. However, a common edge case is that the responder is configured for main mode while the initiator is configured for aggressive mode, causing the exchange to fail before any state is established.
What should I do if I get this 300-410 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 300-410 NAT questions on configuration and troubleshooting.
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?
Static NAT maps one inside address to one outside address.
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