Reliable IPv4 subnetting is not a memorization contest. Start with the number of required addresses, choose the smallest prefix that fits, then use its block size to find each aligned boundary. The same method works for an exam question, a firewall rule, and a real allocation plan.

Short answer: for a conventional IPv4 LAN, add room for the network and broadcast addresses, round up to a power of two, convert that size to a prefix, then verify the network boundary and broadcast address. Never choose a subnet by counting decimal addresses by eye.
Calculate 192.0.2.0/26Practice with the subnet quizVisualize a /24 split

The four-step subnetting method

  1. Count addresses, not only devices. A conventional IPv4 subnet reserves one network address and one directed broadcast address.
  2. Round up to a power of two. For 60 hosts, 62 usable addresses are needed, so choose a 64-address block.
  3. Convert the block size to a prefix. A 64-address IPv4 block leaves six host bits: 26 = 64, so the prefix is /26.
  4. Check the aligned boundaries. A /26 increments by 64 in the last octet: 0, 64, 128, and 192.

A /26 has mask 255.255.255.192. Its first address is the network identifier; its last address is the directed broadcast; the addresses strictly between them are the conventional host range. The method describes ordinary multi-access IPv4 LANs; the point-to-point /31 exception is covered in the /31 and /32 guide.

Worked exercise: split a /24 for four teams

A training lab owns documentation prefix 192.0.2.0/24 and needs four equal team networks. Dividing 256 addresses into four equal parts produces 64 addresses each, therefore four /26 networks. The boundaries are exact; there are no gaps and no overlap.

TeamNetworkUsable host rangeBroadcast
Platform192.0.2.0/26192.0.2.1–192.0.2.62192.0.2.63
Operations192.0.2.64/26192.0.2.65–192.0.2.126192.0.2.127
Security192.0.2.128/26192.0.2.129–192.0.2.190192.0.2.191
Growth192.0.2.192/26192.0.2.193–192.0.2.254192.0.2.255

The fourth block is deliberately unassigned. Keeping it as one aligned /26 lets the organization later give a team up to 62 conventional hosts without renumbering the first three teams. If the requirement changes, use the VLSM Planner rather than forcing unequal teams into an equal-size design.

Avoid the common boundary mistakes

  • Starting a /26 at 192.0.2.32: 32 is not a /26 boundary. It belongs to 192.0.2.0/26, whose broadcast is 192.0.2.63.
  • Calling 64 the host count: a conventional /26 has 64 total addresses and 62 usable host addresses.
  • Using the next subnet's network address as a host: 192.0.2.64 begins the second /26; it is not part of the first usable range.
  • Changing the prefix without rechecking capacity: a /27 has only 30 conventional usable hosts. It cannot fit a team that needs 60 hosts.

Check your answer before you deploy

  1. Confirm the prefix has enough addresses for current devices, gateways, and deliberate growth.
  2. Use the CIDR Calculator to verify each network, broadcast, mask, and usable range.
  3. Run the planned blocks through the Subnet Overlap Detector before adding routes, VPN selectors, or cloud peering.
  4. Keep contiguous allocations together when future route aggregation matters; do not summarize across a gap.
  5. Record provider-reserved addresses separately for cloud subnets, because their usable count can be lower than the conventional IPv4 calculation.

Primary sources

  • RFC 4632 defines CIDR addressing and aggregation.
  • RFC 950 defines the traditional IPv4 subnet and broadcast model.
  • RFC 5737 reserves 192.0.2.0/24 for documentation examples.