DHCP glossary

What is a DHCP lease?

A DHCP lease is a time-limited binding that a Dynamic Host Configuration Protocol server grants to a client for an IP address and related settings. It lets the server reclaim and reuse addresses, because the client must renew the lease before it expires or stop using the address.

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A DHCP lease is a time-limited binding that a Dynamic Host Configuration Protocol server grants to a client for an IP address and related settings, enabling the server to reclaim and reuse addresses once the lease expires or is released. The lease process follows a four-step exchange—Discover, Offer, Request, and Acknowledge—with clients renewing at 50% of lease time (T1) and rebinding at 87.5% (T2) if renewal fails, as defined in RFC 2131. Lease duration significantly impacts network operations, network efficiency, and security: longer leases reduce renewal traffic and improve resilience during outages but can exhaust address pools on networks with transient clients, while shorter leases free addresses quickly but increase server load and leave less recovery time during failures.

  • The DHCP lease exchange occurs in four distinct phases—Discover, Offer, Request, and Acknowledge—with clients automatically renewing at timer T1 (50% of lease time) and rebinding to any server at timer T2 (87.5%) if the original server does not respond.
  • Long lease times on guest Wi-Fi networks risk scope exhaustion when devices depart but retain active leases, forcing new clients to fall back to self-assigned link-local addresses until bindings naturally expire.
  • The lease table serves as a critical security and forensic record linking IP addresses to specific devices at precise points in time, making lease history retention essential for incident response and preventing stale DNS records or firewall rules from targeting wrong devices after address reuse.

DHCP lease at a glance

AttributeValue
CategoryNetwork protocol mechanism
Defined inRFC 2131
Protocol and portUDP ports 67 (server) and 68 (client) for DHCPv4
OSI layerApplication layer
Primary useAssigning IP addresses temporarily so they can be reclaimed and reused
Related termsDHCP, DHCP scope, DHCP reservation, DORA, IP address management

How DHCP lease works

A lease begins when a client completes the DHCP exchange and lasts for a duration the server chooses. The client then tracks timers to keep the address or give it up.

  1. Discover and offer: The client broadcasts a request for a server, and a server replies with an offered address and a proposed lease duration.
  2. Request and acknowledge: The client requests the offered address, and the server confirms with an acknowledgment that starts the lease and records the binding.
  3. Renewal at T1: By default, at 50 percent of the lease time (timer T1), the client asks the original server to extend the lease.
  4. Rebinding at T2: If renewal gets no answer, at 87.5 percent of the lease time (timer T2) the client broadcasts a request to any server.
  5. Expiration or release: If no server extends the lease, the client must stop using the address. A client may also release the lease early, which frees the address immediately.

The server stores each lease, including the client identifier, address and expiry, in its lease database, often called a lease table. Lease length is set by the administrator, usually per scope, as described in RFC 2131.

Why DHCP lease matters in enterprise networks

Lease time controls how quickly an address pool recovers. A long lease keeps traffic low and survives short server outages, but addresses held by departed devices stay unavailable until they expire. On networks with many transient clients, such as guest Wi-Fi, long leases can exhaust a scope even though few devices are actually present.

A short lease frees addresses fast and keeps records current, but it raises renewal traffic and leaves clients with less time to ride out a server failure. Because clients begin renewing at half the lease time by default, a server outage longer than the remaining time causes clients to lose addresses and connectivity.

Leases also matter for security and visibility. The lease table is often the only record linking an IP address to a device at a point in time, so incident responders rely on it, and losing or shortening its history makes tracing activity harder. Address reuse also means stale DNS records or firewall rules tied to an old lease can point to the wrong device. Matching lease time to client behavior and retaining lease logs avoids these problems.

DHCP lease vs DHCP reservation

A lease is a temporary binding that expires unless renewed, while a reservation is a configured rule that tells the server to always give the same address to a specific client. What is DHCP Reservation?

AttributeDHCP leaseDHCP reservation
DurationLimited by lease time and renewed by the clientPersistent until an administrator removes it
Address assignedAny free address in the scope, which may change over timeA fixed address matched to a client identifier such as a MAC address
Created byThe DHCP exchange between client and serverAn administrator
Still uses a leaseYes, by definitionYes, the client still receives and renews a lease for the reserved address

DHCP lease vs Static IP address

A lease is an address the server grants and can reclaim, while a static address is configured by hand on the device and involves no DHCP exchange. What is Static IP address?

AttributeDHCP leaseStatic IP address
Assignment methodAutomatic through DHCPManual configuration on the device
ExpirationExpires unless renewedDoes not expire
Reclaiming addressesServer returns expired addresses to the poolAdministrator must track and release them
Conflict riskLower when the server tracks all bindingsHigher if the address falls inside a dynamic range

Common DHCP lease issues

A scope with a multi-day lease on guest Wi-Fi fills with bindings from devices that left hours ago. New clients then fail to get an address and fall back to self-assigned link-local addresses until old leases expire.

When many clients obtained leases at the same time, their renewal timers fire together. After a server restart or a long outage this can produce bursts of requests and brief failures to renew.

If a server loses its lease database or a failover pair is misconfigured, it may offer addresses that clients still hold. The result is address conflicts, with intermittent connectivity and duplicate address warnings on affected hosts.

A lease of a few minutes leaves clients little time to continue working during a server failure. Devices lose connectivity soon after the server goes down because they cannot renew before expiry.

When dynamic DNS updates are tied to leases, expired or released leases that are not cleaned up leave records pointing at addresses now used by other devices. Name lookups then return the wrong host.

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DHCP lease FAQ

Related terms

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DHCP (Dynamic Host Configuration Protocol)

DHCP (Dynamic Host Configuration Protocol) is the standard mechanism to dynamically assign IP addresses within a network.

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DHCP Scope

A DHCP scope defines the range of IP addresses and related configuration settings that a DHCP server can assign to devices on a network segment.

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DHCP Reservation

A DHCP reservation ensures that a specific device receives the same IP address whenever it requests an address from a DHCP server.

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DORA process

The DORA process is the four-step sequence of Discover, Offer, Request, and Acknowledge messages exchanged between DHCP client and server to assign an IP address.

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IP Address Exhaustion

IP address exhaustion occurs when a network runs out of available IP addresses to assign to devices, limiting its ability to accommodate new connections.

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DHCP Relay Agent

A DHCP relay agent forwards DHCP messages between clients and servers on different network subnets, enabling centralized DHCP services.

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IP Address Conflict

An IP address conflict occurs when two or more devices on a network are assigned the same IP address, disrupting network communication.

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Dynamic DNS (DDNS)

Dynamic DNS (DDNS) automatically updates DNS records when a device's IP address changes, keeping domain names associated with the correct network addresses.

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