What is the Overlay Transport Virtualization site VLAN used for?

What is the Overlay Transport Virtualization site VLAN used for?
A . to allow the join interfaces at different sites to communicate
B . to detect devices at the site that are not capable of OTV
C . to allow multiple site AEDs to communicate with each other
D . to detect other OTV edge devices in the site

Answer: D

Explanation: The edge device performs OTV functions: it receives the Layer 2 traffic for all VLANs that need to be extended to remote locations and dynamically encapsulates the Ethernet frames into IP packets that are then sent across the transport infrastructure. It is expected that at least two OTV edge devices are deployed at each data center site to improve the resiliency.

Reference: http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Data_Center/DCI/whitepaper/DCI3_OTV_Intro/DCI_1.html