D-Link xStack DES-3800 Series, User Manual

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xStack DES-3800 Series Layer 3 Stackable Fast 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 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.
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- 5. 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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