200-301 · Question #1333
How does frame switching function on a switch?
The correct answer is A. floods unknown destinations to all ports except the receiving port. When a switch receives a frame with an unknown destination MAC address, it floods the frame out all ports except the receiving port.
Question
How does frame switching function on a switch?
Options
- Afloods unknown destinations to all ports except the receiving port
- Bmodifies frames that contain a known source VLAN
- Crewrites the source and destination MAC address
- Dbuffers and forwards frames with less than 5 CRCs
How the community answered
(16 responses)- A88% (14)
- B6% (1)
- D6% (1)
Why each option
When a switch receives a frame with an unknown destination MAC address, it floods the frame out all ports except the receiving port.
A switch learns MAC addresses and stores them in its MAC address table; if a frame arrives with a destination MAC address not in the table, the switch floods the frame to all ports in the same VLAN, excluding the ingress port, to find the destination.
A Layer 2 switch primarily forwards frames based on destination MAC addresses and VLAN membership, not by modifying frames based on a known source VLAN.
Rewriting source and destination MAC addresses is a function of a router or devices performing Network Address Translation (NAT), not standard Layer 2 frame switching.
A switch checks for CRC errors to ensure frame integrity and drops corrupt frames, but the number of CRCs is not a forwarding criterion; frames with any CRC errors are typically discarded.
Concept tested: Layer 2 switching unknown unicast behavior
Source: https://www.cisco.com/c/en/us/support/docs/lan-switching/ethernet-switches/10574-5.html
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