IPv6 Planner
Enter your assigned IPv6 prefix (e.g. /48 or /56) and the target subnet size (typically /64). I compute how many subnets fit, the subnet bits, a suggested hierarchy and example prefixes. Fully local.
Suggested hierarchy
| Level | Prefix | Count | Bits | Holds |
|---|
Classic rule: /48 per site → /56 per building (256 per site) → /64 per VLAN (256 per building). The nibble (4 bits) keeps every level readable in hexadecimal.
Example subnets
| # | Prefix | Compressed |
|---|
Subnets are numbered by incrementing the subnet field of the prefix. With
nibble alignment, each hex digit of the prefix maps to a level of the hierarchy,
so 2001:db8:0:0000, 0001,
0002… read at a glance.
Runs locally in your browser · no sign-up · nothing leaves your browser
How it works
The planner takes the IPv6 prefix your ISP or RIR assigned you (for example 2001:db8::/48) and a target subnet size (typically /64) and works out the whole plan: how many subnets fit (2^(target − assigned)), how many subnet bits you use, how many /64s the block contains in total and the first example prefixes, already numbered and compressed per RFC 5952.
It also suggests the classic IPv6 addressing hierarchy: /48 per site → /56 per building → /64 per VLAN, with 256 blocks at each step. The tool warns when the subnet bits are not a multiple of 4, because splitting on nibble boundaries (/48, /52, /56, /60, /64) makes every level of the plan correspond to a full hexadecimal digit, so prefixes can be read at a glance.
Example: splitting 2001:db8::/48 into /64 subnets
- Subnet bits:
64 − 48 = 16, a multiple of 4, so the plan is nibble-aligned. - Available subnets:
2^16 = 65,536/64 blocks, one per VLAN or segment. - Subnets are numbered by incrementing the subnet field:
2001:db8::/64,2001:db8:0:1::/64,2001:db8:0:2::/64… - With the suggested hierarchy, that /48 also supports 256 /56 buildings with 256 /64 VLANs each.