In which VLAN does the switch not add an 802.1Q tag to frames over a trunk link?

The switch does not add an 802.1Q tag to frames over a trunk link in the native VLAN. The native VLAN, which is typically VLAN 1 by default in many Cisco devices, is a special VLAN where untagged frames are allowed to be transmitted over trunk links. This means that when a frame is sent from the native VLAN, it does not carry any VLAN tagging information, allowing it to be processed without the need for an 802.1Q tag.

When a switch receives untagged frames on a trunk port, it assumes that these frames belong to the native VLAN. This behavior is particularly significant in environments where a mix of tagged and untagged traffic exists, as it provides a means for devices that do not support VLAN tagging to communicate over trunk links.

Other options are associated with different VLAN behaviors. VLAN 1 is often the default VLAN but does not specifically indicate exclusion from tagging on trunk links. VLAN 1005, while a valid VLAN, also does not pertain to the native VLAN concept. The unassigned option does not refer to a specific VLAN but rather indicates that no VLAN is designated for a specific operation, which doesn’t directly relate to trunk link behavior. Therefore, the distinctive characteristic of the