Which of the following technologies would an Internet Service Provider use to support overlapping customer VLAN ID’s over transparent LAN services?

A.
802.1q tunneling

B.
ATM

C.
SDH

D.
IP Over Optical Networking

E.
ISL

Explanation:

Understanding How 802.1Q Tunneling Works:
The 802.1Q tunneling feature supports secure virtual private networks (VPNs). 802.1Q tunneling enables service providers to keep traffic from different customers segregated in the service provider infrastructure while significantly reducing the number of VLANs required to support the VPNs. 802.1Q tunneling allows multiple customer VLANs to be carried by a single VLAN on the Catalyst 6000 family switch without losing their unique VLAN IDs.
When you configure 802.1Q tunneling on the Catalyst 6000 family switch, traffic to be tunneled comes into the switch from an 802.1Q trunk port on a neighboring device and enters the switch through a port configured to support 802.1Q tunneling (a tunnel port). When the tunnel port receives traffic from an 802.1Q trunk port, it does not strip the 802.1Q tags from the frame header but, instead, leaves the 802.1Q tags intact and puts all the received 802.1Q traffic into the VLAN assigned to the tunnel port. The VLAN assigned to the tunnel port then carries the tunneled customer traffic to the other neighboring devices participating in the tunnel port VLAN. When the tunneled traffic is received by an 802.1Q trunk port on a neighboring device, the 802.1Q tag is stripped and the traffic is removed from the tunnel.
Reference:
http://www.cisco.com/en/US/products/hw/switches/ps700/products_configuration_guide_chapter09186a008007fa06.html