Q-in-Q Tunneling for Transparent Layer 2 Service

AC

Q-in-Q tunneling adds a service VLAN tag before the customers 802.1Q VLAN tags. The Juniper Networks Junos operating system implementation of Q-in-Q tunneling supports the IEEE 802.1ad standard.

In Q-in-Q tunneling, as a packet travels from a customer VLAN (C-VLAN) to a service provider's or data center VLAN (S-VLAN), another 802.1Q tag for the appropriate S-VLAN is added before the C-VLAN tag. The C-VLAN tag remains and is transmitted through the network. As the packet leaves the S-VLAN in the downstream direction, the S-VLAN 802.1Q tag is removed.

With the push option, a packet retains its tag and an additional VLAN tag is added.

With the swap option, the incoming tag is replaced with an S-VLAN tag. (This is VLAN translation.)

Q-in-Q tunneling is a technique that allows service providers to provide Layer 2 VPN services to their customers by encapsulating customer traffic within provider VLANs. The provider VLANs are then transported across the provider network, allowing multiple customer VLANs to be transported across a single provider link.

In this scenario, the Q-in-Q tunnel will be used to provide a transparent Layer 2 service between two remote locations of the customer. The Q-in-Q tunneling will be used on the two provider edge MX Series routers that connect to the customer's CE devices.

Let's go through the given options and see which ones are true:

A. As traffic enters the Q-in-Q tunnel on the core-facing interface on the ingress PE device, a push operation is performed.

This statement is true. In Q-in-Q tunneling, a push operation is performed on the ingress PE device, which means that the customer VLAN tag is encapsulated within a provider VLAN tag. This allows multiple customer VLANs to be transported across a single provider link.

B. As traffic passes through intermediary P routers in the Q-in-Q tunnel, a push operation is performed.

This statement is false. In Q-in-Q tunneling, the push operation is only performed on the ingress PE device, not on the intermediary P routers. The P routers only transport the provider VLANs across the provider network.

C. As traffic passes through intermediary P routers in the Q-in-Q tunnel, a swap operation is performed.

This statement is false. In Q-in-Q tunneling, the swap operation is only performed on the egress PE device, not on the intermediary P routers. The egress PE device removes the provider VLAN tag and forwards the customer VLAN tag to the customer's CE device.

D. As traffic enters the Q-in-Q tunnel on the core-facing interface on the ingress PE device, a swap operation is performed.

This statement is false. A swap operation is not performed on the ingress PE device. Instead, a push operation is performed, as explained in option A.

Therefore, the correct answers are A and C.