D-Link xStack DGS-3420 Series Reference Manual page 95

xStack® DGS-3420 Series Layer 2 Managed Stackable Gigabit Switch Web UI Reference Guide
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 basically 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.
Q-in-Q 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 Q-in-Q VLAN tagged packet.
802.1Q
SPVLAN (TPID
CEVLAN Tag
Destination + Service
Source Address (TPID + Ether Type Payload
Address Provider VLAN
Customer VLAN
Tag)
Tag)
Consider the example below:
Figure 4-28 QinQ example window
In this example, the Service Provider Access Network switch (Provider edge switch) is the device creating and
configuring Q-in-Q 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.
Regulations for Q-in-Q VLANs
1. Some rules and regulations apply with the implementation of the Q-in-Q VLAN procedure.
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