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 Phase 2 lifetime values are mismatched, causing one peer to expire the SA before the other.

  Why this is correct

  If Phase 2 lifetimes differ, one peer may initiate rekey while the other still considers the old SA valid, leading to a rekey collision or failure. The error 'IKE Phase 2 rekey failed' typically occurs when the rekey request is rejected or times out due to mismatched lifetimes or proposals. Ensuring both peers use identical Phase 2 lifetimes and proposals resolves this specific issue.

• ✗

  Perfect Forward Secrecy (PFS) is disabled on one peer and enabled on the other.

  Why it's wrong here

  PFS mismatch typically causes Phase 2 negotiation to fail entirely, not just rekey failures. If one peer requires PFS and the other does not, the initial Phase 2 will fail, and the tunnel would not establish. Since the tunnel is up and only rekey fails, PFS is likely configured consistently, and the issue is more specific to lifetime mismatches or SA timing.

• ✗

  The Phase 1 lifetime values are mismatched on the two peers.

  Why it's wrong here

  Mismatched Phase 1 lifetimes would affect how often Phase 1 renegotiates, not Phase 2 rekey failures. Phase 2 rekeying uses the Phase 2 lifetime and the existing IKE SA. While a Phase 1 mismatch can cause tunnel drops, the specific error 'IKE Phase 2 rekey failed' points to issues within the IPsec SA rekey process, not the IKE SA lifetime.

• ✗

  The IKE Phase 1 encryption algorithms are different on the two peers.

  Why it's wrong here

  Different Phase 1 encryption algorithms would prevent Phase 1 from completing, so no tunnel would form. The scenario indicates the tunnel is established and only Phase 2 rekey fails, which means Phase 1 is working. Thus, the problem is isolated to Phase 2 parameters such as lifetimes or proposals, not Phase 1 encryption.