Which design consideration must be made when using IPv6 overlay tunnels?
A. Overlay tunnels that connect isolated IPv6 networks can be considered a final IPv6 network architecture.
B. Overlay tunnels should only be considered as a transition technique toward a permanent solution.
C. Overlay tunnels can be configured only between border devices and require only the IPv6 protocol stack.
D. Overlay tunneling encapsulates IPv4 packets in IPv6 packets for delivery across an IPv6 infrastructure.
I agree, tunneling IPv6 should be replaced in the future by a permanent IPv6 routed infrastructre. In addition to this, IPv6 tunneling required the IPv4 stack as transport layer as well, hence answer C is incorrect.
Correct answer is B.
https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9500/software/release/16-10/configuration_guide/ipv6/b_1610_ipv6_9500_cg/configuring_ipv6_over_ipv4_gre_tunnels.html
“The use of overlay tunnels should be considered as a transition technique toward a network that supports both the IPv4 and IPv6 protocol stacks or just the IPv6 protocol stack.”