Cover Exactly the Addresses You Specify
Enter the first and last address of an inclusive IPv4 or IPv6 range. Read all result rows together: their union covers the requested range with no gaps and no extra addresses, using the fewest CIDR blocks. This is useful when a firewall, allowlist or address inventory accepts CIDRs instead of start and end addresses.
Worked Example: 10.0.0.10 Through 10.0.0.50
These 41 addresses require six aligned blocks:
| CIDR | First Address | Last Address | Addresses |
|---|---|---|---|
10.0.0.10/31 | 10.0.0.10 | 10.0.0.11 | 2 |
10.0.0.12/30 | 10.0.0.12 | 10.0.0.15 | 4 |
10.0.0.16/28 | 10.0.0.16 | 10.0.0.31 | 16 |
10.0.0.32/28 | 10.0.0.32 | 10.0.0.47 | 16 |
10.0.0.48/31 | 10.0.0.48 | 10.0.0.49 | 2 |
10.0.0.50/32 | 10.0.0.50 | 10.0.0.50 | 1 |
The /31 rows cover two addresses each; the /32 covers the final address. These describe address membership, not recommended LAN sizes. One 10.0.0.0/26 would contain the range, but would also include .0–.9 and .51–.63, so it is not an exact result.
Splitting, Comparing & Summarizing
Split Subnet divides a parent into equal child prefixes. Compare checks containment and overlap. Analyze & Summarize merges only the exact union of pasted CIDRs, including mixed inventories analyzed separately by address family. It does not fill gaps to create a larger supernet.
Use the VLSM Subnet Planner when the goal is enough usable hosts in each LAN. Use the subnet calculator to inspect one block’s mask and address boundaries.