IPv6 Multicast Calculator
Build an IPv6 multicast address from a scope and group ID, and decode what the flag and scope fields mean.
About IPv6 Multicast Calculator
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.
Formula
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.
- flags
- 0 for IANA-assigned, 1 for transient groups
- scope
- How far the traffic is allowed to propagate
Worked example
With the default values below, IPv6 Multicast Calculator returns Multicast Address of ff15::1234. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Scopeone of 1 — Interface-local, 2 — Link-local, 4 — Admin-local, 5 — Site-local, 8 — Organisation-local, e — Global
- 5 — Site-local
- Group ID (hex)
- 1234
- Transient (dynamically assigned) group
- Yes
Results
- Multicast Address
- ff15::1234
- Scope Meaning
- Site-local — bounded by the site
- Flags Nibble
- 0x1 (transient)
- Ethernet MAC Mapping
- 33:33:00:00:12:34
Step by step
- 1Values used
- 2IPv6 Multicast
- 3Multicast Address= ff15::1234
- 4Scope Meaning= Site-local — bounded by the site
- 5Flags Nibble= 0x1 (transient)
- 6Ethernet MAC Mapping= 33:33:00:00:12:34
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is IPv6 Multicast calculated?
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.
Why does IPv6 Multicast matter?
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.
What values do I need to enter?
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.