CCSM Advanced VPN Troubleshooting Practice Question
Exhibit
IKE_DEBUG: [VPN] Peer identity mismatch: Expected: 192.168.1.1, Received: 10.0.0.5
Refer to the exhibit. What is the most likely reason for this error?
⚠ Common exam trap
Candidates often troubleshoot general routing or phase 2 IPsec settings when peer identity mismatches are actually triggered by intermediary NAT devices altering source addresses.
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
✓
A NAT device is modifying the source IP address of the IKE packets.
A peer identity mismatch occurs when the identity provided by the remote gateway during IKE negotiation does not match the identity configured in the local gateway's VPN community. This is often caused by a NAT device sitting between the gateways, changing the packet source IP. Recognizing this mismatch is crucial for determining if the issue is a configuration error or a network topology problem.
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 VPN tunnel is configured for dynamic IP addresses.
Why it's wrong here
If a tunnel is configured for dynamic IPs, the gateway expects a specific identity format (like a certificate or string) rather than a specific static IP. An identity mismatch here would indicate a failure of the ID authentication, not an issue with the IP addressing itself.
- ✓
A NAT device is modifying the source IP address of the IKE packets.
Why this is correct
When a NAT device sits between two VPN peers, the original source IP is translated. The receiving gateway sees the NAT IP instead of the peer's actual static IP, leading to a identity mismatch error because the gateway expects the original source IP configured in the community.
- ✗
The license on the peer gateway has expired.
Why it's wrong here
An expired license would prevent the gateway from initiating any encrypted connections. It would not cause an identity mismatch error during the IKE negotiation process; instead, the connection attempt would likely be rejected by the peer or time out completely without providing an identity error.
- ✗
The local gateway is using an outdated IKE proposal set.
Why it's wrong here
Outdated proposals cause a negotiation mismatch regarding security algorithms, not an identity mismatch. If the proposal set were the issue, the logs would indicate an 'encryption proposal mismatch' or 'hash algorithm mismatch,' not a peer identity mismatch.
Visual reference
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Check Point exam blueprint
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