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300-410 Practice Question: Runs the following command to troubleshoot an…
A network engineer runs the following command to troubleshoot an IPsec Site-to-Site VPN issue:
R1# debug crypto ipsec *Mar 1 00:02:34.567: IPSEC(sa_request): , (key eng. msg.) src=10.0.0.1, dst=10.0.0.2, src_proxy=192.168.1.0/255.255.255.0/0/0, dst_proxy=192.168.2.0/255.255.255.0/0/0, *Mar 1 00:02:34.567: IPSEC(validate_proposal): transform proposal (esp-3des esp-sha-hmac) not supported for proxy 192.168.1.0/255.255.255.0/0/0 *Mar 1 00:02:34.567: IPSEC(validate_proposal): proposal doesn't match! *Mar 1 00:02:34.568: IPSEC(create_sa): SA created with (0x1234, 0x5678) but no inbound or outbound SPI
What does this output indicate?
⚠ Common exam trap
Cisco often tests the distinction between IKE phase 1 and phase 2 failures; the trap here is that candidates might assume the SA creation message with SPIs indicates success, but the 'no inbound or outbound SPI' line reveals the SA is incomplete, pointing to a transform set mismatch rather than ACL or IKE phase 1 issues.
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 transform set on the remote peer does not match the local transform set, causing IPsec SA negotiation to fail.
The debug output shows that the IPsec SA request is generated, but the transform proposal (esp-3des esp-sha-hmac) is rejected with 'not supported for proxy'. This indicates that the remote peer does not support or is configured with a different transform set, causing the proposal to fail validation. The SA is created with placeholder SPIs (0x1234, 0x5678) but no actual inbound/outbound SPI, confirming negotiation failure due to transform set mismatch.
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 IPsec SA is established successfully with ESP 3DES and SHA.
Why it's wrong here
The output says 'proposal doesn't match' and 'no inbound or outbound SPI', indicating failure.
- ✓
The transform set on the remote peer does not match the local transform set, causing IPsec SA negotiation to fail.
Why this is correct
The debug explicitly states the proposal is not supported, meaning a mismatch in transform set.
- ✗
The ACL for the crypto map is misconfigured, causing the traffic to not match.
Why it's wrong here
The debug shows src_proxy and dst_proxy, indicating the ACL matched, but the transform set is the issue.
- ✗
The IKE phase 1 SA is not established before IPsec negotiation.
Why it's wrong here
The debug does not mention IKE phase 1; it focuses on IPsec transform validation.
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.
Go deeper
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.