Describe how the DHCP lease is obtained?

Very basic and fundamental process of DHCP lease is that when a DHCP enabled client requests for an IP the DHCP server provides the client IP with desired gateway and DNS. and Before the lease expires either DHCP server renews or extends the lease or the client renews the IP address to carry on the task on network.

1. The DHCP client requests an IP address by broadcasting 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 configuration information for lease to the client. If no DHCP server responds to the client request, the client can proceed in two ways:

   • If it is a Windows 2000–based client, and IP auto-configuration has not been disabled, the client self-configures an IP address for its interface.

   • If the client is not a Windows 2000–based client, or IP auto-configuration has been disabled, the client network initialization fails. The client continues to resend DHCPDiscover messages in the background (four times, every 5 minutes) until it receives a DHCPOffer message from a DHCP server.

3. The client indicates acceptance of the offer by selecting the offered address and replying to the server with a DHCPRequest message.

4. The client is assigned the address and the DHCP server sends a DHCPAck message, approving the lease. Other DHCP option information might be included in the message.

5. Once the client receives acknowledgment, it configures its TCP/IP properties using any DHCP option information in the reply, and joins the network.

In rare cases, a DHCP server might return a negative acknowledgment to the client. This can happen if a client requests an invalid or duplicate address. If a client receives a negative acknowledgment (DHCPNak), the client must begin the entire lease process again.

The DHCP client requests an IP address by broadcasting a DHCPDiscover message to the local subnet

The client is offered an address when a DHCP server responds with a DHCPOffer message containing an IP address and configuration information for lease to the client

The client indicates acceptance of the offer by selecting the offered address and replying to the server with a DHCPRequest message.

The client is assigned the address and the DHCP server sends a DHCPAck message, approving the lease

Once the client receives acknowledgment, it configures its TCP/IP properties using any DHCP option information in the reply, and joins the network.

DORA process

D  Discover

O  Offer

R  Request

A Acknoweldge