Lease Renewals

The renewal process occurs when a client already has a lease, and needs to renew that lease with the server. To ensure that addresses are not left in an assigned state when they are no longer needed, the DHCP server places an administrator-defined time limit, known as a lease duration, on the address assignment.

Halfway through the lease period, the DHCP client requests a lease renewal, and the DHCP server extends the lease. If a computer stops using its assigned IP address (for example, if a computer is moved to another network segment or is removed), the lease expires and the address becomes available for reassignment.

The renewal process occurs as follows:

1. The client sends a request to the DHCP server, asking for a renewal and extension of its current address lease. The client sends a directed request to the DHCP server, with a maximum of three retries at 4, 8, and 16 seconds.
   • If the DHCP server can be located, it typically sends a DHCP acknowledgment message to the client. This renews the lease.
   • If the client is unable to communicate with its original DHCP server, the client waits until 87.5 percent of its lease time elapses. Then the client enters a rebinding state, broadcasting (with a maximum of three retries at 4, 8, and 16 seconds) a DHCPDiscover message to any available DHCP server to update its current IP address lease.
2. If a server responds with a DHCPOffer message to update the client's current lease, the client renews its lease based on the offering server and continues operation.
3. If the lease expires and no server has been contacted, the client must immediately discontinue using its leased IP address. The client then proceeds to follow the same process used during its initial startup to obtain a new IP address lease.

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