Which of the following items may cause IPSec VPN establishment to fail? (Multiple choice)

Question

Options

• AThe route to the opposite intranet is unreachable
• BInconsistent packaging modes
• CSupported encryption algorithms are inconsistent
• DThe ACL does not contain the business addresses that both ends need to communicate with.

• A
  100% (28)

Explanation

All four options are valid failure causes because IPSec VPN establishment depends on every layer of the communication stack working correctly. A fails the VPN because if the peer's subnet is unreachable at the routing level, IKE negotiation packets never arrive - the tunnel can't even begin. B (packaging/encapsulation modes: Tunnel vs. Transport) must match on both endpoints; a mismatch means peers form incompatible Security Associations and the tunnel is rejected during IKE Phase 2. C causes failure during IKE Phase 1 negotiation - both peers must agree on a common cipher suite (e.g., AES, 3DES); if no overlap exists, the proposal is rejected entirely. D fails because the ACL defines "interesting traffic" that triggers and protects the VPN; if the business subnets aren't listed, the traffic is never encrypted or sent through the tunnel, effectively breaking communication even if the tunnel itself establishes.

Since all choices are correct, there are no distractors to dismiss - every listed factor is a genuine IPSec dependency.

Memory tip: Think of IPSec as a handshake ceremony with four prerequisites - Route (can we even reach each other?), Mode (are we speaking the same dialect?), Algorithm (do we agree on the secret language?), Traffic (do we know what to protect?). Acronym: RMAT - if any piece is missing, the VPN fails.

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