Double Vlans - D-Link DES-3528 User Manual

xStack DES-3528 Series Layer 2 Stackable Fast Ethernet Managed Switch User Manual

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
Consider the example below:
In this example, the Service Provider Access Network switch (Provider edge switch) is the device creating and
configuring Double VLANs with different SPVIDs for specific customers (say Customer A and Customer B). Both
CEVLANs (Customer VLANs), CEVLAN 10 are tagged with the SPVID 100 (for Customer A) and SPVID 200 (for
Customer B) on the Service Provider Access Network, thus being a member of two VLANs on the Service Provider's
network. In this way, the Customer can retain their normal VLAN ID's and the Service Provider can seperate multiple
Source SPVLAN
Address Service
VLAN Tag)
Figure 7- 6. Double VLAN Example
(TPID + 802.1Q CEVLAN
Provider (TPID + Customer VLAN
Tag)
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Tag Ether Payload
Type