D-Link xStack DGS-3426P User Manual - Double Vlans

xStack DGS-3400 Series Layer 2 Gigabit Ethernet Managed Switch 

Double VLANs 

Double or Q-in-Q VLANs allow network providers to expand their VLAN configurations to place customer VLANs within a 

larger inclusive VLAN, which adds a new layer to the VLAN configuration. This lets large ISP's create L2 Virtual Private 

Networks and also create transparent LANs for their customers, which will connect two or more customer LAN points without 

over-complicating configurations on the client's side. Not only will over-complication be avoided, but also now the administrator 

has over 4000 VLANs in which over 4000 VLANs can be placed, therefore greatly expanding the VLAN network and enabling 

greater support of customers utilizing multiple VLANs on the network. 

Double VLANs are basically VLAN tags placed within existing IEEE 802.1Q VLANs which we will call SPVIDs (Service 

Provider VLAN IDs). These VLANs are marked by a TPID (Tagged Protocol ID), configured in hex form to be encapsulated 

within the VLAN tag of the packet. This identifies the packet as double-tagged and segregates it from other VLANs on the 

network, therefore creating a hierarchy of VLANs within a single packet.  

Here is an example Double VLAN tagged packet. 

Destination Address  Source Address  SPVLAN    (TPID  + 

Service Provider 

VLAN Tag) 

802.1Q CEVLAN Tag 

(TPID + Customer VLAN 

Tag) 

Ether Type  Payload 

Consider the example below: 

Figure 7- 8. Double VLAN Example 

In this example, the Service Provider Access Network switch (Provider edge switch) is the device creating and configuring 

Double VLANs. Both CEVLANs (Customer VLANs) 10 and 11, are tagged with the SPVID 100 on the Service Provider Access 

Network and therefore belong to one VLAN on the Service Provider’s network, thus being a member of two VLANs. In this way, 

the Customer can retain its normal VLAN and the Service Provider can congregate multiple Customer VLANs within one 

SPVLAN, thus greatly regulating traffic and routing on the Service Provider switch. This information is then routed to the Service 

Provider’s main network and regarded there as one VLAN, with one set of protocols and one routing behavior.  

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