Work out dual stack addressing plan instantly with clear inputs, formula shown and shareable results.
A dual-stack plan numbers both families on the same topology. IPv4 needs a bit budget: sites multiplied by subnets per site rounded up to a power of two tells you how many subnet bits to reserve. IPv6 is allocated by prefix instead of by host count — a /48 per site yields 65,536 /64 links — and the site prefixes then aggregate into one shorter prefix for the whole estate.
Dual-stack budget
IPv4 subnets = sites x subnets per site; subnet bits = ceil(log2(subnets)); IPv6 /64s per site = 2^(64 - site prefix); aggregate = site prefix - ceil(log2(sites))
SLAAC and many IPv6 features assume 64 host bits. Using a longer prefix on a LAN breaks autoconfiguration, so subnet on nibble boundaries above /64 instead.
Encoding the VLAN ID into the IPv6 subnet field, for example 2001:db8:1:20::/64 for VLAN 20, makes troubleshooting far easier than unrelated numbering.