hardMultiple ChoiceObjective-mapped
300-410 Practice Question: An engineer configures IPsec between two routers
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?
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 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.
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.
- ✗
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.
Quick reference
VPN Protocol Comparison
| Protocol | Port | Encryption | Authentication | Use Case |
|---|---|---|---|---|
| IKEv2 / IPsec | UDP 500 / 4500 | AES-256 | Certificates / PSK | Site-to-site & remote access |
| SSL / TLS VPN | TCP 443 | TLS 1.3 | Certificates / MFA | Clientless remote access |
| L2TP / IPsec | UDP 1701 | AES (IPsec) | PSK / Certificates | Legacy remote access |
| WireGuard | UDP 51820 | ChaCha20 | Public keys | Modern high-performance VPN |
| PPTP | TCP 1723 | MPPE (weak) | MS-CHAPv2 | Legacy — avoid in production |
PPTP is considered insecure. IKEv2/IPsec and SSL VPN are the current recommended options.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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