5 min read
2026-02-20
When using VLSM, allocate subnets for the largest segments first, then carve the remaining space into smaller ones.
The number of hosts in a subnet is always 2^n - 2. Plan your needs by rounding up to the nearest power of two.
Do not use up all address space at once. Leave free blocks between subnets for future expansion.
Place related subnets in contiguous blocks. This allows route aggregation and simplifies the routing table.
For each subnet, record:
Purpose (servers, users, management)
Address range and mask
VLAN identifier
Responsible administrator
Forgetting to subtract the network and broadcast addresses
Creating overlapping subnets
Not leaving room for growth
Check your subnets with the Subnet Calculator.
See also: IP Calculator, MAC Lookup