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Difficulty: EasyL2 Switching Concepts and MAC Table Operation

Switch SW1 receives a unicast frame on ingress port GigabitEthernet0/2. The frame contains a source MAC address of 7069.5a12.1234 and a destination MAC address of 0011.2233.4455. The MAC address table of SW1 currently has no entries. Which two actions does the switch perform upon receiving this frame? (Select two.)

  1. The switch records the source MAC address 7069.5a12.1234 and ingress port GigabitEthernet0/2 in its MAC address table.Answer
  2. B
    The switch forwards the frame directly to its configured default gateway to resolve the destination address.
  3. The switch floods the frame out all active ports assigned to the same VLAN, excluding port GigabitEthernet0/2.Answer
  4. D
    The switch floods the frame out all active ports assigned to the VLAN, including port GigabitEthernet0/2.
  5. E
    The switch drops the frame immediately because the destination MAC address is missing from its MAC address table.

Answer

The switch records the source MAC address on ingress port GigabitEthernet0/2 in its MAC address table and floods the frame out all operational ports in the same VLAN except GigabitEthernet0/2.
When an Ethernet switch receives a frame, it executes two key processes: learning and forwarding. First, it reads the source MAC address (7069.5a12.1234) and maps it to the receiving interface (GigabitEthernet0/2) in its MAC address table. Second, because the destination MAC address (0011.2233.4455) is not listed in its table, the frame is treated as an unknown unicast frame. The switch floods the frame out every operational port in the VLAN except the ingress port where the frame was received.

Step-by-Step Solution

1
Examine the ingress frame's source MAC address and ingress interface.
The switch adds an entry for source MAC 7069.5a12.1234 mapped to port GigabitEthernet0/2.
Layer 2 switches perform dynamic MAC learning by recording the source address of every incoming frame.
2
Examine the ingress frame's destination MAC address against the MAC address table.
Destination MAC 0011.2233.4455 is not found in the table, identifying the frame as an unknown unicast frame.
An empty MAC table contains no matching entry for the destination.
3
Apply Layer 2 forwarding rules for an unknown unicast frame.
The frame is flooded out all active ports in the same VLAN except ingress port GigabitEthernet0/2.
Flooding ensures the unknown destination host receives the frame without retransmitting traffic out the ingress port.

Key Concept

L2 Switching Concepts and MAC Table Operation
Estimated Time:1m 0s
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Topics

L2 Switching Concepts and MAC Table Operation

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