Which standard defines VLAN tagging on trunk links?

Which standard defines VLAN tagging on trunk links?

• A. 802.1Q
• B. 802.1D
• C. 802.3
• D. 802.11

Answer: (A)

VLAN tagging on trunk links is defined by IEEE 802.1Q. This standard introduces a 4-byte tag inserted into Ethernet frames on trunk connections, allowing switches to identify which VLAN the frame belongs to as it travels over a single physical link. The tag carries the VLAN identifier (12 bits) along with priority information, and a specific TPID value (0x8100) marks the frame as tagged. Untagged frames on a trunk are associated with the native VLAN, which helps maintain compatibility with devices or configurations that don’t tag every frame. This tagging enables multiple VLANs to share the same physical link while keeping their traffic isolated. In contrast, other options serve different roles: 802.1D defines Spanning Tree Protocol, which prevents loops in a network; 802.3 covers Ethernet standards for framing and access methods; and 802.11 is about wireless LAN standards.

VLAN tagging on trunk links is defined by IEEE 802.1Q. This standard introduces a 4-byte tag inserted into Ethernet frames on trunk connections, allowing switches to identify which VLAN the frame belongs to as it travels over a single physical link. The tag carries the VLAN identifier (12 bits) along with priority information, and a specific TPID value (0x8100) marks the frame as tagged. Untagged frames on a trunk are associated with the native VLAN, which helps maintain compatibility with devices or configurations that don’t tag every frame. This tagging enables multiple VLANs to share the same physical link while keeping their traffic isolated.

In contrast, other options serve different roles: 802.1D defines Spanning Tree Protocol, which prevents loops in a network; 802.3 covers Ethernet standards for framing and access methods; and 802.11 is about wireless LAN standards.