ZyXEL Communications GS-2750, User Manual

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GS-2750 User’s Guide
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H A P T E R
21
VLAN Stacking
This chapter shows you how to configure VLAN stacking on your Switch. See the chapter on
VLANs for more background information on Virtual LAN
21.1 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.
21.1.1 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.