IPv6 CIDR Range Calculator
Tip: If you include /prefix in the first field, that prefix is used automatically.
What this IPv6 range calculator does
This tool takes an IPv6 address and prefix length, then calculates the full network range for that subnet. In practical terms, it tells you the first address, last address, network ID, subnet mask, and total number of addresses. That is useful when you are planning routing, delegating subnets, validating cloud network settings, or checking firewall rules.
How IPv6 ranges work
IPv6 addresses are 128 bits long. The prefix length (for example /64) tells you how many leading bits are fixed
for the network portion. The remaining bits are host/interface bits.
- Network bits: fixed bits that identify the subnet.
- Host bits: variable bits that can represent addresses inside that subnet.
- Total addresses:
2^(128 - prefix).
Example
For 2001:db8:abcd::1/64, the network is 2001:db8:abcd::/64.
The range begins at 2001:db8:abcd:: and ends at
2001:db8:abcd:0:ffff:ffff:ffff:ffff.
Understanding the output fields
- Network (CIDR): canonical subnet representation.
- Network Address: first address in the block (all host bits set to 0).
- Last Address: highest address in the block (all host bits set to 1).
- Expanded Form: full 8 hextets, each 4 hex digits.
- Compressed Form: shorthand notation using IPv6 zero compression rules.
- Subnet Mask (hex): 128-bit mask shown in IPv6 format.
Common IPv6 prefix sizes
/32
Typically allocated to large organizations or providers for further subnetting.
/48
A common site-level allocation, giving many /64 subnets.
/56
Often delegated to residential customers for multiple LANs.
/64
The standard subnet size for most LANs and SLAAC environments.
/128
A single host address (useful for loopbacks and point assignments).
Best practices for subnet planning
- Use consistent prefix boundaries across environments to simplify operations.
- Document allocated ranges and reserve room for future growth.
- Keep route summarization in mind when assigning site and region blocks.
- Validate every entered prefix before deploying to production.
Final note
IPv6 notation can look intimidating at first, but subnet math becomes straightforward once you focus on the prefix length. Use this calculator whenever you need fast, accurate range boundaries for network design, troubleshooting, or audits.