KB.15.15

Figure 75 VLANs in a QinQ configuration

Customer VLANs (referred to as C-VLANs by the IEEE 802.1ad specification) are not used to make

any forwarding decisions inside the provider network where customer frames get assigned to

service VLANs (S-VLANs). Inside the provider cloud, frames are forwarded based on the S-VLAN

tag only, while the C-VLAN tag remains shielded during data transmission. The S-VLAN tag is

removed when the frame exits the provider network, restoring the original customer frame.

Features and benefits

• Increases the VLAN space in a provider network or enterprise backbone.

• Reduces the number of VLANs that a provider needs to support within the provider network

for the same number of customers.

• Enables customers to plan their own VLAN IDs, without running into conflicts with service

provider VLAN IDs.

• Provides a simple Layer 2VPN solution for small-sized MANs (Metropolitan Area Networks)

or intranets.

• Provides for customer traffic isolation at Layer 2 within a Service Provider network.

Configuring QinQ

QinQ must be configured on all the devices and ports participating in the provider bridge. Typically,

customer facing ports are configured as untagged members of S-VLANs and provider facing ports

are configured as tagged members of S-VLANs. Per the IEEE 802.1ad specification, there is no

condition binding port types (customer or provider) to untagged or tagged S-VLAN memberships.

Therefore, when configuring QinQ tunnelling on the switch, you would first configure per-port

S-VLAN membership (tagged or untagged), and then configure the port type as

customer-network or provider-network, depending on the device to which the switch port

is connected.

NOTE: A customer-network port can receive S-VLAN tagged frames if the customer and provider

agree on the S-VID association for that customer and the customer device is capable of sending

S-VLAN tagged frames.

To configure QinQ take the following steps on all participating provider switches:

1. Enable QinQ on the device, selecting the appropriate QinQ mode (S-VLAN or mixed VLAN

mode).

2. Save the configuration and reboot the switch.

3. Configure S-VLANs and assign per port VLAN membership.

4. Configure port-types for all of the switch ports that carry QinQ traffic across the network.

Configuring QinQ 323