What is the difference between 802.1Q tagging and 802.1QinQ tagging?

• A. 802.1Q adds a VLAN tag; 802.1QinQ stacks another tag to carry customer VLANs across a provider network
• B. 802.1Q is older; 802.1QinQ is deprecated
• C. 802.1Q uses IPv6; 802.1QinQ uses IPv4
• D. 802.1Q encrypts frames; 802.1QinQ does not

Answer: (B)

The key idea is how many VLAN tags are used and what each tag represents. With 802.1Q, an Ethernet frame gets a single VLAN tag that marks which VLAN it belongs to as it moves through a switched network. 802.1QinQ (often called Q-in-Q) takes that a step further by adding a second VLAN tag around the already tagged frame. The inner tag preserves the customer's VLAN ID, while the outer tag is used by the service provider to carry and isolate many customer VLANs across its backbone. This nesting lets providers transport multiple customer networks over the same physical network without mixing their VLAN spaces.

So the difference isn’t about IPv4 vs IPv6 or encryption—that’s not part of how VLAN tagging works. It’s about single-tag tagging versus stacking a second tag to extend VLAN separation across provider networks. The notion that one is deprecated isn’t accurate; both concepts are still in use, with QinQ simply enabling a broader, nested VLAN strategy.