Work out multicast address range instantly with clear inputs, formula shown and shareable results.
IPv4 multicast lives in 224.0.0.0/4. Inside it, 224.0.0.0/24 is link-local control traffic that routers never forward, 232.0.0.0/8 is source-specific multicast, 233.0.0.0/8 is GLOP, and 239.0.0.0/8 is administratively scoped space for private use — the multicast equivalent of RFC 1918. Carving a block gives you 2^(32-prefix) group addresses to allocate to applications.
Multicast block
groups = 2^(32 - prefix); first = base AND mask; last = first + groups - 1
239.0.0.0/8. It is administratively scoped, so it will not clash with global assignments and can be filtered cleanly at organisation boundaries.
Those groups are for control protocols such as OSPF and PIM. They are sent with TTL 1 and must never be forwarded off the local link.