In IPSec, if the Security ACL does not match the actual data flow to be protected, which of the following consequences will occur?

Question

Options

• AIKE SA cannot be established
• BIPSec VPN services are blocked
• CNo data flow triggers IKE negotiation
• DIPSec SA cannot be established

• A
  4% (1)
• B
  9% (2)
• C
  83% (19)
• D
  4% (1)

Explanation

When the Security ACL doesn't match the actual data flow, the ACL fails to identify any packets as "interesting traffic" - the classification IPSec uses to trigger IKE negotiation. Since no packet is recognized as needing protection, no packet ever initiates the IKE handshake process. This makes C the direct, root-level consequence: the negotiation never starts because nothing fires the trigger.

Why the distractors are wrong:

• A (IKE SA cannot be established) is a downstream effect of C, not the immediate cause - IKE SA fails because negotiation was never triggered, not directly because of the ACL mismatch.
• D (IPSec SA cannot be established) is even further downstream; IPSec SA failure is a consequence of IKE SA never being established, making it two steps removed from the root cause.
• B (IPSec VPN services are blocked) is imprecise - services aren't actively blocked by a security rule; they simply never start because the trigger condition is never met.

Memory tip: Think of the Security ACL as a "bouncer list" at the door of IKE negotiation. If the real traffic isn't on the list, the bouncer never lets anyone in to start the handshake - the party (VPN tunnel) never happens, not because it was refused, but because no one ever knocked.

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