Which of the following descriptions about IGMP Snooping are correct? (Multiple choice)

Question

Options

• AThe IGMP Snooping device monitors the IGMP Leave message and the IGMP Membership Report message to determine whether the port needs to send specific multicast data
• BThe function of IGMP Snooping is to establish and maintain Layer 3 multicast forwarding entries, and guide multicast data to be forwarded on demand
• CIn IGMP Snooping, you can manually configure member ports
• DWhen the router port receives a new general group query, it will refresh the aging timer

• A
  78% (35)
• B
  22% (10)

Explanation

A is correct because IGMP Snooping works by listening ("snooping") on IGMP Membership Report messages (indicating a host wants to join a group) and IGMP Leave messages (indicating a host is leaving), using these to decide which ports should receive specific multicast streams.

C is correct because IGMP Snooping supports static (manual) configuration of member ports - useful when hosts don't send IGMP reports but still need to receive multicast traffic.

D is correct because router ports maintain aging timers, and receiving a new General Query from the multicast router resets that timer, confirming the router is still active and the port should remain a router port.

B is wrong because it incorrectly states IGMP Snooping operates at Layer 3. IGMP Snooping is a Layer 2 feature that builds and maintains Layer 2 multicast forwarding entries on a switch. Layer 3 multicast forwarding entries are the responsibility of multicast routing protocols (e.g., PIM), not IGMP Snooping.

Memory tip: The word "Snooping" tells you everything - it listens to Layer 2 traffic to make smart forwarding decisions. If an answer says IGMP Snooping does anything at Layer 3, it's wrong.

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