CCSM Advanced VPN Troubleshooting Practice Question

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 community is not configured with the correct encryption domain.

  Why it's wrong here

  An incorrect encryption domain might cause traffic to be dropped or not encrypted, but it would not produce 'no proposal chosen' during Quick Mode. That error specifically points to a mismatch in Phase 2 parameters. Encryption domain issues typically manifest as traffic not matching the VPN or being sent in clear text.

• ✓

  The Phase 2 encryption or integrity algorithms do not match between peers.

  Why this is correct

  The error 'no proposal chosen' in Quick Mode indicates that the peers cannot agree on a Phase 2 proposal. This typically happens when the encryption, integrity, or PFS settings differ. Aligning the Phase 2 proposal on both gateways resolves the negotiation failure. Phase 1 success confirms that the IKE SA is fine, so the mismatch is specifically in the IPsec SA parameters.

• ✗

  The pre-shared secret is incorrect.

  Why it's wrong here

  An incorrect pre-shared secret would cause Phase 1 to fail, typically with a 'no valid SA' or authentication error. Since Phase 1 completes successfully, the pre-shared secret is correct. The failure is in Phase 2, which negotiates IPsec SA parameters, so the issue lies in the Phase 2 proposal, not the pre-shared key.

• ✗

  The peer's IP address is not reachable.

  Why it's wrong here

  If the peer's IP were unreachable, Phase 1 would not complete because IKE runs over UDP port 500/4500. The scenario states Phase 1 completes, meaning the peers can communicate. Thus, reachability is not the issue; the Phase 2 failure is due to incompatible proposal settings.