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A tagged frame in a VLAN configuration indicates that it belongs to a specific VLAN. This tagging process is crucial for the proper operation of VLANs, as it allows network devices to identify which VLAN the frame is associated with as it traverses through switches and routers. Tagging is done using the IEEE 802.1Q standard, which adds a VLAN tag to the Ethernet frame, containing the VLAN ID.

When a switch receives a tagged frame, it examines the VLAN ID specified in the tag to determine how to process the frame. By doing so, the switch can maintain the separation of different VLANs within the same physical network infrastructure. This capability is essential for scenarios where multiple VLANs share the same network links, preventing cross-traffic between VLANs and ensuring that each VLAN’s broadcast traffic remains confined to its own group.

In contrast, untagged frames (not belonging to any VLAN) are treated differently; they will usually be placed in the switch’s default or native VLAN unless configured otherwise. Tagged frames provide the necessary information for properly managing network traffic in a multi-VLAN environment, which is vital for effective network segmentation and security.