200-301 · Question #1341
How does MAC learning function on a switch?
The correct answer is C. adds unknown source MAC addresses to the address table. MAC learning on a switch involves examining the source MAC address of incoming frames and recording them in the MAC address table along with the port they were received on.
Question
How does MAC learning function on a switch?
Options
- Aprotects against denial of service attacks
- Bsends frames with unknown destinations to a multicast group
- Cadds unknown source MAC addresses to the address table
- Dsends a retransmission request when a new frame is received
How the community answered
(42 responses)- A2% (1)
- B2% (1)
- C90% (38)
- D5% (2)
Why each option
MAC learning on a switch involves examining the source MAC address of incoming frames and recording them in the MAC address table along with the port they were received on.
While MAC address tables are involved in network security, MAC learning itself is not primarily a DoS protection mechanism.
Frames with unknown destinations are typically flooded to all ports (except the receiving one), not sent to a multicast group.
When a switch receives a frame, it inspects the source MAC address and the port on which the frame arrived. If this source MAC address is not already in the switch's MAC address table (also known as CAM table or forwarding table), the switch adds an entry for that MAC address associated with the specific input port, thereby 'learning' its location for future forwarding decisions.
A switch does not send retransmission requests; that is a function of higher-layer protocols or physical layer error detection, not basic MAC learning.
Concept tested: Switch MAC address learning function
Source: https://www.cisco.com/c/en/us/support/docs/switches/catalyst-6500-series-switches/10570-41.html
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