This post is in continuance to the previous post on DHCP fundamentals (Link) –
Now, we will understand DORA process in detail.
DORA process in DHCP is stands for following message flows between the client and the server.
Now let’s take a look what happens when these messages are exchanged between DHCP Client and Server. 2 key items should be kept in mind which are also important from interview point of view as well. These are –
- Network layer broadcast and
- Data Link Layer broadcast.
DHCP client sends out a DHCP Discover message to find out the DHCP server. DHCP discover message is a layer 2 broadcast as well as layer 3 broadcast.
Fields in DHCP Discover Message:
Hence from the above fields it is clear DHCP Discover message is a Network Layer and Data Link Layer Broadcast.
DHCP server receives the DHCP discover message from client and sends back the DHCP offer message with field information as below:
Hence from above field it is clear that DHCP offer message is a layer 2 unicast but still as layer 3 broadcast.
DHCP client receives the DHCP offer from DHCP server and sends back a DHCP Request message with following fields:
Above fields concludes that DHCP request message is also a layer 2 unicast and a layer 3 broadcast.
Once the DHCP client sends the request to get the Offered IP address, DHCP server responds with an acknowledge message towards DHCP client with below fields:
From above fields substantiates that DHCP Acknowledge is a layer 2 unicast but still a layer 3 broadcast.
For more details on the information you must get familiar with the DHCP header fields. Few important fields from DHCP header for our reference are as below –