DHCP Lease Process

The first time that a  client (with DHCP enabled) attempts to join a network, it automatically follows an initialization process to obtain a lease from a DHCP server.

1. The DHCP client requests an IP address by broadcasting a message (known as a DHCPDiscover message) to the local subnet.
2. The client is offered an address when a DHCP server responds with a DHCPOffer message containing an IP address, and associated configuration information, available for lease to the client.
3. The client selects the offered address and replies to the server with a DHCPRequest message. Alternatively, the DHCP client might request the IP address that was previously assigned.
4. The client is assigned the address, and the DHCP server sends an acknowledgment message (DHCPAck) approving the lease. Other DHCP option information, such as default gateway and DNS server addresses, might be included in the message.

After the client receives acknowledgment, it configures its TCP/IP properties using any DHCP option information in the DHCPAck message and completes the initialization of TCP/IP.

If no DHCP server responds to the client request, the client can proceed in one of two ways:

1. If APIPA is enabled, the client self-configures a unique IP address in the range 169.254.0.1 through 169.254.255.254.
2. If APIPA has been disabled, the client network initialization fails. The client continues to re-send DHCPDiscover messages in the background until it receives a valid lease from a DHCP server. The client makes four attempts to obtain a lease, one every five minutes.