1. Size the largest IPv4 allocation first
Suppose a segment needs 50 conventional IPv4 hosts. Six host bits provide 64 addresses and 62 usable hosts, so choose /26. Five host bits would provide only 30 usable hosts. A /24 can contain four equal /26s.
Within 192.0.2.0/24, the /26 boundaries are .0, .64, .128 and .192. The first block runs from 192.0.2.0 to 192.0.2.63, with hosts .1 through .62. The next begins immediately at .64; it does not begin at .63.
2. Use VLSM when segments need different sizes
For segments needing 50, 25 and 10 hosts, reserve 192.0.2.0/26 (62 usable), 192.0.2.64/27 (30 usable) and 192.0.2.96/28 (14 usable). Their address ranges are .0–.63, .64–.95 and .96–.111, leaving .112–.255 unallocated.
Allocate the largest blocks first to reduce fragmentation. Check alignment as well as capacity: 192.0.2.80/27 belongs to the .64/27 block and is not a separate subnet. In the planner, generate /26s and subdivide selected leaves to visualize a hierarchy, then inspect the allocations you intend to use.
3. Plan IPv6 by prefix hierarchy
For 2001:db8::/32, allocating /48 site prefixes yields 65,536 sites. Each /48 can hold 65,536 /64 subnet prefixes. This is prefix arithmetic, not a recommendation that every network should receive the same site size.
IPv6 has no broadcast address, so do not subtract a network and broadcast pair as you would for a conventional IPv4 LAN. A /64 is common for SLAAC-enabled LANs; other prefix lengths have specific uses, such as /127 point-to-point router links described in RFC 6164.
4. Verify the plan before assigning addresses
Check that every child is inside the parent, no siblings overlap, and masks match capacity. Confirm whether you are looking at inclusive address counts or usable hosts. Use the range converter to verify first and last addresses independently of the tree.
These calculators operate on the addresses you supply; they do not discover routes, check live reachability, or reserve addresses in an IPAM system. Export the plan for review and apply your organization’s addressing policies before changing a network.