Option A: Correct — both terminal and interface security are important.

Option C: Correct — CAPWAP supports DTLS encryption for secure tunnel communication.

Option D: Correct — intranet security design considers both wired and wireless.

Option B: Incorrect — traffic suppression (such as broadcast suppression) is implemented using rate limiting or storm control, not by shutting down interfaces. Shutting down interfaces would disrupt legitimate traffic too.

Correct answer: B