Selective QinQ

Selective QinQ, also called VLAN stacking or QinQ stacking, is performed based on interfaces and VLAN IDs. In addition to basic QinQ functions, selective QinQ has the following functions:

VLAN ID-based selective QinQ: adds outer VLAN tags based on inner VLAN IDs.
802.1p priority-based selective QinQ: adds outer VLAN tags based on 802.1p priorities in inner VLAN tags.
Traffic policy-based selective QinQ: adds outer VLAN tags based on traffic policies so that differentiated services can be provided based on service types.

Selective QinQ is an extension of basic QinQ and provides more flexibility. The difference is as follows:

Basic QinQ: adds the same outer VLAN tag to all packets arriving at a Layer 2 interface.
Selective QinQ: adds different outer VLAN tags to packets arriving at a Layer 2 interface based on inner VLAN tags.

As shown in Figure 1, Department 1 and Department 2 have multiple offices.

Figure 1 Networking diagram of selective QinQ

**Table 1** VLAN plan
Device	Interface	VLAN ID Range	Outer VLAN ID
PE1	Port1	2 to 500	10
	Port1	1000 to 2000	20
	Port2	100 to 500	10
PE2	Port1	1000 to 4094	20
PE2	Port2	500 to 2500	20

Department 1 uses VLANs 2 to 500.
Department 2 uses VLANs 500 to 4094.
Port1 on PE1 receives packets from VLANs of Department 1 and Department 2 simultaneously.

Selective QinQ is configured on PE1 and PE2 in the following way to implement communication within each department and isolate the two departments.

Outer VLAN tags for packets received on interfaces of PE1 and PE2 are configured according to Table 1.
Port3 on PE1 and Port3 on PE2 allow packets of VLAN 20 to pass.