Which IPv6 prefix is used for 6to4 transition addresses?

• A. 2002::/16
• B. 2001:0db8::32
• C. ::ffff/96
• D. fc00::/7

Answer: (A)

6to4 uses a special IPv6 prefix that signals the packet is part of a 6to4 tunnel, allowing IPv6 traffic to ride over the IPv4 Internet by embedding the IPv4 address into the IPv6 address. The prefix for these 6to4 addresses is 2002::/16. When an IPv6 address begins with 2002, the next 32 bits encode the sender’s IPv4 address in hexadecimal, which enables routers on the path to forward the traffic to the corresponding 6to4 endpoint over IPv4.

Other prefixes serve different purposes: 2001:0db8::/32 is reserved for documentation and examples, not actual routing; ::ffff/96 is used for IPv4-mapped IPv6 addresses, representing IPv4 addresses inside IPv6 for dual-stack hosts; fc00::/7 is the Local Unique Address range for private use, not for 6to4.