Which prefix is used for Teredo IPv6 addresses?

• A. 2001:db8::/32
• B. fc00::/7
• C. 2002::/16
• D. 2001:0000::/32

Answer: (D)

Teredo addresses are a special IPv6 tunneling scheme that lets hosts behind NATs reach the IPv6 Internet by carrying IPv6 over IPv4. They are identified by a fixed prefix, which marks an address as Teredo.

The Teredo prefix is 2001:0000::/32. That means any IPv6 address starting with 2001:0000 is a Teredo-Tunnel address, with the remaining bits encoding details like the Teredo server, flags, and the embedded IPv4/port information needed for NAT traversal.

The other prefixes point to different concepts: 2001:db8::/32 is reserved for documentation and not routable on the public Internet; fc00::/7 is for Unique Local Addresses used privately; 2002::/16 is the 6to4 prefix used for another automatic tunneling method. Since the question asks specifically which prefix designates Teredo addresses, the correct choice is 2001:0000::/32.