A Layer 2 device, such as a switch, primarily examines the destination MAC address in the Ethernet frame header to determine where to forward the data onward. It uses the destination MAC address to identify the appropriate port or path within the local network to send the frame. Additionally, the source MAC address is also examined to update the device's MAC address table with the originating device's location. Other fields like the Ethernet type may be examined for protocol identification but do not influence the forwarding decision at Layer 2.
Key Ethernet Frame Header Information Examined by Layer 2 Devices:
- Destination MAC address: Critical for forwarding frames to the correct device within the LAN.
- Source MAC address: Used to update the MAC address table for learning the sender's location.
- Ethernet type (optional): Indicates the payload protocol but is not used for forwarding decisions.
- Optional VLAN Tag: Used for VLAN segregation and Quality of Service (QoS) handling when present.
In summary, the destination MAC address is the most important piece of information a Layer 2 device examines to forward data onward efficiently within a network.
