27.1.1 Overview

VLAN tunneling functionality aggregates, or tunnels, VLANs for multiple users into another VLAN. IEEE 802.1Q VLAN tags can be stacked to transparently forward frames belonging to other VLANs, within a single VLAN. Tunnels are capable of multipoint connections that connect three or more locations.

The figure below provides an overview of VLAN tunneling, including an example application of wide-area Ethernet service. With VLAN tunneling, VLAN tags can be stacked to distinguish VLANs within a VLAN-tunneled network.

This example application uses a Layer 2 VPN service, which is a wide-area Ethernet service. VLAN tunneling functionality is used for the Switch. With VLAN tunneling, VLAN tags can be stacked to distinguish VLANs within a VLAN-tunneled network. A port handling a user site is called an access line, and a port connected within the VLAN-tunneled network is called a backbone line. VLAN tags are added to frames from an access line, and the frames are then forwarded to the backbone line. Likewise, VLAN tags are removed from frames from a backbone line, and the frames are then forwarded to an access line.

Figure 27-1 VLAN Tunneling Overview (Example of Wide-Area Ethernet Service Application)