Updated 8 hours ago
You don't own your IP address.
When your device connects to a network and receives an IP address from DHCP, you're getting a lease—a temporary assignment with an expiration date. You can stay as long as the lease is valid, but you'll need to renew periodically to keep it.
This isn't a limitation. It's how networks stay healthy in an unreliable world.
Why Leases Exist
The temporary nature of DHCP leases handles a fundamental reality: devices vanish, servers fail, and requirements change.
Address Reclamation
IP addresses in a subnet are finite. If addresses were permanently assigned, every device that ever connected would hold its address forever—even after it leaves.
When you shut down your laptop gracefully, it sends a DHCPRELEASE message: "I'm done with this address; you can give it to someone else." But devices don't always leave gracefully. Batteries die. Cables get unplugged. Visitors walk away with their phones still technically connected.
Leases ensure that addresses return to the available pool after a predictable time, even when devices vanish without saying goodbye.
Configuration Propagation
Network administrators need to make changes: moving devices to different VLANs, updating DNS servers, rolling out new services. Leases provide a natural propagation mechanism.
When leases renew, the DHCP server can provide updated parameters. Over time—without manual intervention—every device on the network picks up the new configuration.
Mobility
Your smartphone might connect to your home WiFi, then a coffee shop, then your office. Each network grants you a temporary address appropriate for its subnet. When you leave, the lease eventually expires, and that address becomes available for the next person.
What a Lease Contains
A DHCP lease includes:
- The IP address assigned to your device
- The subnet mask and default gateway
- DNS server addresses
- The lease duration
- Two critical timers: T1 (renewal time) and T2 (rebinding time)
Your device doesn't passively sit with this lease until it expires. It actively manages the lease through a lifecycle designed to maintain connectivity while adapting to change.
The Lease Lifecycle: Optimism to Desperation
A DHCP lease progresses through distinct phases, each representing an escalating assumption about what might have gone wrong.
Acquisition (DORA Process)
The lifecycle begins when your device requests an IP address using the DORA process: Discover, Offer, Request, Acknowledge. Once the DHCP server sends the final ACK, your device enters the BOUND state—it has a valid lease and can communicate on the network.
At this moment, two critical timers start counting down: T1 and T2.
Renewal at T1 (50% of Lease Duration)
The T1 timer defaults to 50% of the total lease duration. For an 8-day lease, T1 expires after 4 days.
When T1 expires, your device transitions to RENEWING state and sends a unicast DHCPREQUEST directly to the original DHCP server. This is the polite approach—a direct conversation with the server it already knows.
If the server responds with a DHCPACK, the lease is renewed. Your device resets its timers and returns to BOUND state. You won't notice this happened.
If the server doesn't respond, your device stays in RENEWING state and keeps trying. Connectivity isn't interrupted—you're still using your IP address normally.
Rebinding at T2 (87.5% of Lease Duration)
If your device still hasn't renewed by T2, it assumes the original server is gone. Maybe it crashed, was decommissioned, or lost network connectivity.
Now your device transitions to REBINDING state and broadcasts a DHCPREQUEST to the entire local network: "I have this IP address and I need to extend my lease. Can any DHCP server help me?"
This is the desperate phase. The device has given up on its preferred relationship and is asking anyone who'll listen. In enterprise networks with redundant DHCP servers, a backup can step in without interrupting connectivity.
If any server responds with a DHCPACK, the lease is renewed. If you receive a DHCPNAK (negative acknowledgment), you must release your current address and start over with a fresh DORA process.
Expiration: The Eviction
If no DHCP server responds by the time the lease expires, your device must stop using the IP address immediately. You lose connectivity and must restart the entire DHCP process by broadcasting a DHCPDISCOVER.
Active connections—file transfers, video streams, SSH sessions—drop without warning.
This scenario is rare because the multi-phase system provides multiple opportunities to renew before expiration. But when it happens, it's abrupt.
Lease Durations by Environment
Different environments use different lease times based on device behavior patterns.
Home Networks: 24 Hours
Most residential routers default to 24-hour leases. Devices don't constantly renew, but if you remove a device, its address becomes available the next day. For home networks with small device counts and large address pools, this rarely needs changing.
Enterprise Networks: 1-8 Days
Corporate networks use longer leases. An 8-day lease for wired desktops makes sense—these devices are stable and rarely move. Wireless devices often get shorter leases (1-2 days) to accommodate laptop and mobile device mobility.
Public WiFi: 1 Hour or Less
Networks with high turnover—coffee shops, airports, conference centers—use very short leases. Constant device churn means addresses need to return to the pool quickly. The tradeoff is more DHCP traffic, but efficient address reuse outweighs the overhead.
IoT Networks: 12-24 Hours
IoT devices frequently reconnect—smart home devices power cycle or lose WiFi signal. Leases need to be long enough to avoid excessive renewal traffic but short enough to accommodate device turnover.
Manual Lease Management
Sometimes you need to manually intervene, typically when troubleshooting.
Releasing a Lease
Releasing tells the DHCP server you no longer need your IP address, making it immediately available for other devices.
Windows:
Linux:
macOS:
After releasing, your device has no IP address until you request a new lease.
Renewing a Lease
Renewing requests a new lease, either extending your current one or obtaining a new IP address.
Windows:
Linux:
macOS:
When to Use Release/Renew
- Network configuration has changed and you want to pick up new settings immediately
- You're experiencing intermittent connectivity and want a fresh start
- You've joined a different network but your device is clinging to an old IP address
- Network diagnostics suggest a DHCP lease problem
The release/renew cycle restarts the entire DHCP process, which resolves a surprising number of network issues.
The Design Philosophy
The progression from T1 to T2 to expiration is escalating paranoia: try the polite thing first, then get desperate, then give up.
At T1, your device assumes everything is fine and quietly asks its original server to renew. At T2, it assumes the server is gone and broadcasts to anyone listening. At expiration, it accepts defeat and starts over.
This minimizes network traffic in the common case while providing fallbacks for increasingly unlikely failures. Most renewals happen silently at T1. The desperate T2 broadcast and abrupt expiration are safety nets that rarely deploy.
You don't own your IP address. But the lease system ensures that, most of the time, you don't need to care. It handles the impermanence for you, maintaining the illusion of stability while adapting to change underneath.
Frequently Asked Questions About DHCP Leases
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