Capacity planning prevents surprises. You predict future needs and upgrade before running out of bandwidth, ports, or processing power.
What to track: Bandwidth utilization on links, port utilization on switches, CPU and memory on routers and firewalls, VPN tunnel counts, DHCP pool usage.
The capacity planning cycle:
Measure: Collect baseline data over time
Trend: Identify growth patterns
Project: Extrapolate when you'll hit limits
Plan: Budget for upgrades before you need them
Monitoring tools like PRTG, LibreNMS, or Grafana collect historical data. Review trends monthly.