What are three IPv6 transition mechanisms? (Choose three.)

A.
6to4 tunneling

B.
VPN tunneling

C.
GRE tunneling

D.
ISATAP tunneling

E.
PPP tunneling

F.
Teredo tunneling

Explanation:
The key to a successful IPv6 transition is compatibility with the large installed base of IPv4 hosts and routers. Maintaining compatibility with IPv4 while deploying IPv6 will streamline the task of transitioning the Internet to IPv6. This specification defines a set of mechanisms that IPv6 hosts and routers may implement in order to be compatible with IPv4 hosts and routers.
The mechanisms in this document are designed to be employed by IPv6 hosts and routers that need to interoperate with IPv4 hosts and utilize IPv4 routing infrastructures. We eXPect that most nodes in the Internet will need such compatibility for a long time to come, and perhaps even indefinitely. However, IPv6 may be used in some environments where interoperability with IPv4 is not required. IPv6 nodes that are designed to be used in such environments need not use or even implement these mechanisms. The mechanisms specified here include:
Dual IP layer (also known as Dual Stack): A technique for providing complete support for both Internet protocols – IPv4 and IPv6 – in hosts and routers.
Configured tunneling of IPv6 over IPv4: Point-to-point tunnels made by encapsulating IPv6 packets within IPv4 headers to carry them over IPv4 routing infrastructures.
IPv4-compatible IPv6 addresses: An IPv6 address format that employs embedded IPv4 addresses.