Build an IPv6 multicast address from a scope and group ID, and decode what the flag and scope fields mean.
Every IPv6 multicast address starts with ff. The flags nibble marks whether the group is permanently assigned, the scope nibble bounds propagation, and the remaining bits identify the group. Layer 2 delivery uses 33:33 plus the low 32 bits of the address. Scope selection decides whether multicast stays on a VLAN or floods a WAN, and the 33:33 mapping is what you match when hunting multicast storms in a capture.
IPv6 Multicast
A multicast address is ff, then a 4-bit flags nibble, then a 4-bit scope, then the group ID; the Ethernet destination is 33:33 followed by the last 32 bits.
A multicast address is ff, then a 4-bit flags nibble, then a 4-bit scope, then the group ID; the Ethernet destination is 33:33 followed by the last 32 bits. Every IPv6 multicast address starts with ff. The flags nibble marks whether the group is permanently assigned, the scope nibble bounds propagation, and the remaining bits identify the group. Layer 2 delivery uses 33:33 plus the low 32 bits of the address.
Scope selection decides whether multicast stays on a VLAN or floods a WAN, and the 33:33 mapping is what you match when hunting multicast storms in a capture.
This calculator takes 3 inputs: Scope, Group ID (hex), Transient (dynamically assigned) group. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.