DHCP Architecture

DHCP follows the” DORA “process:

DORA means

• D – Discover
• O – Offer
• R – Request
• A – Acknowledgement

Architecture: 

• Client sends  DISCOVER message to  find the DHCP server available in the network.
• Client sends DISCOVER message as broadcast message that uses the UDP port 67 as destination. 
• As applicable DISCOVER message can contain a desired IP address, the last used IP address and/or the lease time duration.
• DHCP server receives the DISCOVER message and will respond with an OFFER message that contains all the network parameters. OFFER message also broadcast message that uses the UDP port 68 as destination.
• When client receives the OFFER message it chooses a certain IP configuration then will send a REQUEST message to the DHCP server to inform that the specified IP address has been chosen. So that Server  will know that the client has chosen the IP address and that will be added to the database with lease time duration.
• The server will then respond with an ACK (Acknowledge) message and the network parameters will be sent to the client.

DHCP assignment:

• Lease Request: Client broadcasts request to DHCP server with a source address of 0.0.0.0 and a destination address of 255.255.255.255. The request includes the MAC address which is used to direct the reply.
• IP lease offer: DHCP server replies with an IP address, subnet mask, network gateway, name of the domain, name servers, duration of the lease and the IP address of the DHCP server.
• Lease Selection: Client receives offer and broadcasts to all DHCP servers that will accept given offer so that other DHCP server need not make an offer.
• The DHCP server then sends an acknowledgement to the client. The client is configured to use TCP/IP.
• Lease Renewal: When half of the lease time has expired, the client will issue a new request to the DHCP server for renewal.