D-Link DGS-6600-48T Configuration Guide - Page 100

Volume 3-Layer 2 Configurations / Chapter 11-VLAN Tunneling • UNI to NNI • CoS Remarking • VLAN-Tunnel TPID • UNI to UNI • UNI to UNI for VLAN Remarking Feature • VLAN Remarking UNI to NNI • NNI to UNI or NNI to NNI Forwarding • Determining the S-VLAN • Determining the Forwarding Port • NNI to UNI • NNI to NNI Chapter Overview VLAN Encapsulation VLAN encapsulation is also known as VLAN stacking or Q-in-Q. VLAN encapsulation inserts a second VLAN (service provider VID, S-VID) as an outer tag for packets that are being transmitted from the Networks-to-Network Interface (NNI). Instead of changing the customer's original VLAN tag information, the VLAN mapping mechanism adds more service provider VLAN tags to traverse the service provider networks. Typically, there is a many-to-one mapping relationship between multiple C-VIDs and the S-VID. At UNI ingress ports, the outer S-Tag is stacked on top of a C-Tag. At UNI egress ports, the outer S-Tag is removed. Figure 11-1 Tagged Frames from UNI to NNI with VLAN Encapsulation Feature DGS-6600 Configuration Guide 100