Compare IPv4 and IPv6 capacity for the same network and size the overhead of running both stacks.
The two stacks are sized independently: IPv4 is constrained by scarcity and needs segment counts, while IPv6 is constrained only by the prefix you were allocated. Running both roughly doubles neighbour tables, routes and monitoring series. Dual stack is the default migration path, and the hidden cost is not addresses but the doubled state on firewalls, load balancers and monitoring systems.
Dual Stack
IPv4 segments = ceil(hosts ÷ (2^(32 − v4 prefix) − 2)); IPv6 /64 subnets = 2^(64 − site prefix).
IPv4 segments = ceil(hosts ÷ (2^(32 − v4 prefix) − 2)); IPv6 /64 subnets = 2^(64 − site prefix). The two stacks are sized independently: IPv4 is constrained by scarcity and needs segment counts, while IPv6 is constrained only by the prefix you were allocated. Running both roughly doubles neighbour tables, routes and monitoring series.
Dual stack is the default migration path, and the hidden cost is not addresses but the doubled state on firewalls, load balancers and monitoring systems.
This calculator takes 4 inputs: Hosts to address, IPv4 prefix per segment, IPv6 site prefix, Extra state entries per host. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.