ZyXEL ES-3148 Guida Utente

ES-3148 User’s Guide

This chapter shows you how to configure VLAN stacking on your Switch. See the chapter on 
VLANs for more background information on Virtual LAN

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. 

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.