Your customer requests that you provide a transparent Layer 2 service between two of their remote locations. This service must allow the customer to pass tagged traffic from multiple VLANs. You decide to use Q-in-Q tunneling on the two provider edge MX Series routers that connect to the customers CE devices.
Which two statements are true? (Choose two.)
Click on the arrows to vote for the correct answer
A. B. C. D.AB
Q-in-Q (also known as VLAN stacking or nested VLANs) is a technique used in Ethernet switching to support multiple VLANs over a single VLAN, allowing service providers to offer Layer 2 VPN services to customers with different VLAN requirements.
In this scenario, the customer needs a transparent Layer 2 service between two remote locations, where multiple VLANs must be supported. To accomplish this, Q-in-Q tunneling will be used on the two provider edge MX Series routers that connect to the customer's CE devices.
Here are the answers to the given question:
A. As traffic leaves the Q-in-Q tunnel, the S-VLAN tag will be removed from the frames.
This statement is correct. When traffic is sent over the Q-in-Q tunnel, the customer's original VLAN tags (C-VLAN tags) are encapsulated with new service provider VLAN tags (S-VLAN tags) before being sent over the provider network. As the frames leave the Q-in-Q tunnel, the S-VLAN tag is removed, and the original C-VLAN tag is used to forward the frames to their destination.
B. As traffic enters the Q-in-Q tunnel, an S-VLAN tag will be added to the frames.
This statement is also correct. When traffic enters the Q-in-Q tunnel, the provider edge routers add a new S-VLAN tag to the frames before forwarding them over the provider network. The S-VLAN tag identifies the customer's VLAN and enables the provider to separate customer traffic belonging to different VLANs.
C. As traffic enters the Q-in-Q tunnel, a C-VLAN tag will be added to the frames.
This statement is incorrect. When traffic enters the Q-in-Q tunnel, the provider edge routers do not add a new C-VLAN tag to the frames. Instead, they add a new S-VLAN tag, which is used to separate customer traffic belonging to different VLANs.
D. As traffic leaves the Q-in-Q tunnel, the C-VLAN tag will be removed from the frames.
This statement is also incorrect. When traffic leaves the Q-in-Q tunnel, the provider edge routers remove the S-VLAN tag, not the C-VLAN tag. The original C-VLAN tag remains in place and is used to forward the frames to their destination.
In summary, Q-in-Q tunneling is used to provide a transparent Layer 2 service between two remote locations, supporting multiple VLANs over a single VLAN. As traffic enters the Q-in-Q tunnel, an S-VLAN tag is added to the frames, and as traffic leaves the Q-in-Q tunnel, the S-VLAN tag is removed. The original C-VLAN tag remains in place throughout the process.