DHCP stands for Dynamic Host Configuration Protocol. DHCP used to provide IP addresses to different Hosts or Client machine present in a Network. DORA is nothing but a sequence of messages which is exchanged between the DHCP Server and Client. DORA stands for mentioned messages :
Now, take a look on this image. This image will clear the sequence of different messages which is used in DORA Process.
DHCP Discover Message
This is the first message which is sent by the DHCP client to discover DHCP Server in the network. This message is broadcast at Network and Data Link Layer.
DHCP Offer Message
DHCP Offer Message is sent by the DHCP Server to DHCP client. In this message, DHCP Server offers an IP address to DHCP client. This message is unicast at Data Link Layer but broadcast at the network layer.
DHCP Request Message
This message is sent from the DHCP client to the DHCP Server. In this message, DHCP client request to DHCP server for the offered IP address. This message is unicast at data link layer but broadcast at the network layer.
DHCP Acknowledgement Message
This is the final message of DHCP DORA Process. This message is sent by the DHCP Server to the DHCP Client. This message is unicast at data link layer but broadcast at the network layer.