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This chapter shows you how to configure VLAN stacking on your Switch. See the chapter on VLANs
for more background information on Virtual LAN
22.1 VLAN Stacking Overview
A service provider can use VLAN stacking to allow it to distinguish multiple customers VLANs, even
those with the same (customer-assigned) VLAN ID, within its network.
Use VLAN stacking to add an outer VLAN tag to the inner IEEE 802.1Q tagged frames that enter the
network. By tagging the tagged frames ("double-tagged" frames), the service provider can manage
up to 4,094 VLAN groups with each group containing up to 4,094 customer VLANs. This allows a
service provider to provide different service, based on specific VLANs, for many different
customers.
A service provider's customers may require a range of VLANs to handle multiple applications. A
service provider's customers can assign their own inner VLAN tags on ports for these applications.
The service provider can assign an outer VLAN tag for each customer. Therefore, there is no VLAN
tag overlap among customers, so traffic from different customers is kept separate.
22.1.1 VLAN Stacking Example
In the following example figure, both A and B are Service Provider's Network (SPN) customers with
VPN tunnels between their head offices and branch offices respectively. Both have an identical VLAN
tag for their VLAN group. The service provider can separate these two VLANs within its network by
adding tag 37 to distinguish customer A and tag 48 to distinguish customer B at edge device 1 and
then stripping those tags at edge device 2 as the data frames leave the network.
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