What information does a switch use to populate its MAC address table?
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Correct answer: ingress frames.
Why this is the answer
A switch learns MAC addresses by examining the source MAC address of frames as they enter (ingress) its ports. When a frame arrives, the switch records the source MAC address and the port it came in on into its MAC address table. This allows the switch to know which port to send future frames out of to reach that specific MAC address. VTP (VLAN Trunking Protocol) and DTP (Dynamic Trunking Protocol) are used for VLAN management and trunk negotiation, respectively, not for populating the MAC address table. Egress frames are frames leaving the switch, and their destination MAC addresses are used for forwarding, not for learning source MAC addresses.
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