Work out DHCP T1 and T2 renewal timers and the renewal load a client population puts on the server.
RFC 2131 has clients renew at half the lease and rebind at seven-eighths of it, so each client generates one renewal every T1 minutes regardless of whether anything changed. Any lease longer than the client's session leaves the address reserved after it disconnects. Halving the lease time doubles server request load and doubles the churn in DNS if you run dynamic updates, while very long leases silently strand addresses in a busy guest network.
DHCP Lease
T1 = lease × 50%, T2 = lease × 87.5%, and renewals per hour = clients × 60 ÷ T1 in minutes.
T1 = lease × 50%, T2 = lease × 87.5%, and renewals per hour = clients × 60 ÷ T1 in minutes. RFC 2131 has clients renew at half the lease and rebind at seven-eighths of it, so each client generates one renewal every T1 minutes regardless of whether anything changed. Any lease longer than the client's session leaves the address reserved after it disconnects.
Halving the lease time doubles server request load and doubles the churn in DNS if you run dynamic updates, while very long leases silently strand addresses in a busy guest network.
This calculator takes 5 inputs: DHCP clients, Lease time, T1 renewal point, T2 rebinding point, Average client online time. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.