If the video gateway needs to perform MAC dimension control, the FW needs to enable the () function.

Question

Options

• AAttack prevention
• BCross-three-layer MAC learning
• CNorth direction
• DSNMP

• A
  5% (1)
• B
  79% (15)
• C
  11% (2)
• D
  5% (1)

Explanation

Cross-three-layer MAC learning allows the firewall to discover and track MAC addresses of hosts that reside in different subnets - i.e., separated by a Layer 3 boundary. Without this feature, the FW can only see MAC addresses within its directly connected Layer 2 segments; enabling it lets the gateway enforce MAC-based dimension control (access policy, authentication, or accounting) on traffic that has already been routed across subnet boundaries, which is essential for video gateway deployments where endpoints may span multiple VLANs or IP segments.

Why the distractors are wrong:

• A (Attack prevention): A threat-mitigation feature (IPS, anti-DDoS, etc.) - controls malicious traffic, not MAC-layer identity management.
• C (North direction): Northbound interfaces are management/API abstractions (e.g., for SDN controllers); they have nothing to do with MAC address learning.
• D (SNMP): A network monitoring and management protocol used for device polling and trap notifications - unrelated to per-device MAC control.

Memory tip: The word "three" in cross-three-layer is your anchor - it means crossing Layer 3 (the network/routing layer) so the firewall can still see Layer 2 MAC addresses. If the gateway controls by MAC but traffic crosses a router, you need this feature to bridge that gap.

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