Teredo is used to transition IPv4 to IPv6 by tunneling IPv6 over which transport protocol?

• A. UDP over IPv6
• B. UDP over IPv4
• C. TCP over IPv4
• D. ICMP over IPv4

Answer: (D)

Teredo is a tunneling method designed to carry IPv6 across IPv4 networks, especially through NATs, by wrapping IPv6 packets inside UDP datagrams that are then sent over IPv4. The key idea is IPv6 over UDP over IPv4. UDP is chosen because it’s lightweight and easier to traverse NATs and firewalls, which helps establish and maintain the tunnel without the overhead of a connection-oriented protocol.

That’s why the transport path is IPv6 payload inside UDP, carried over IPv4. The other options don’t fit: UDP over IPv6 would place UDP on top of IPv6, not over IPv4; UDP over IPv4 without the IPv6 payload wouldn’t fulfill the purpose of Teredo; TCP over IPv4 is connection-oriented rather than the stateless, NAT-friendly tunneling Teredo uses; and ICMP over IPv4 isn’t how Teredo carries IPv6 traffic.