Which prefix identifies IPv6 multicast?
Answer
ff00::/8
Multicast is ff00::/8 — the whole first byte is ff, and the bits that follow encode flags and scope rather than narrowing the prefix. Writing it as /16 is a natural slip because multicast addresses are usually met as ff02::1 and ff02::2, which makes the first two bytes look fixed; ff02::/16 is in fact the link-local multicast range, a subset. The other two prefixes are real and belong elsewhere: fe80::/10 is link-local unicast and fc00::/7 is unique local.