I manage a school network with hundreds of devices and want to clear the DHCP leases. I changed the lease duration to four hours and was thinking of deleting the leases on Friday evening. Would that give devices enough time to renew before Monday?
Can I clear all DHCP leases over a weekend?
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Not necessarily. Changing the duration on the server does not shorten leases that clients already hold. A device with an existing seven day lease could continue using that address for days unless it renews sooner.
Deleting the server's records doesn't tell clients to stop using their addresses either. The server could then hand an address to another device while the original client is still using it, creating a conflict. I wouldn't purge the records on that schedule.
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What are you trying to fix by clearing them, and what DHCP server are you using? If you're changing the address scheme, cleaning up stale records, or dealing with an exhausted pool, those call for different plans. You may not need to delete anything.
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If the goal is to move clients to a new configuration, plan around the longest existing lease, not just the new four hour setting. Let clients renew and receive the new settings, then check what is still active. Old records can age out rather than being purged.
Some devices may be offline during the change, so allow for them to return later and verify the server's behavior for the particular scope and configuration.
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Rebooting switches or access points may cause some clients to reconnect and request DHCP, but it also interrupts the network and doesn't guarantee every device will discard its existing lease. Treat it as a maintenance action, not a reliable way to clear all client state.
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If leases have already been deleted, check whether your DHCP server supports address conflict detection before issuing addresses. Ping checks can help catch some addresses still in use, but they're not foolproof because devices can be offline or block ping. Don't rely on that as a substitute for preserving lease records.
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sOft_reset_pending:
Clients normally try to renew halfway through their current lease and try rebinding later, often at 87.5 percent. Those timers come from the lease they already received.