This post is in continuance to the previous post on DHCP fundamentals
Now, we will understand the DORA process in DHCP in detail –
DHCP DORA process stands for the following message flows between the client and the server.
Below diagram depicts the message flow between the DHCP client and the DHCP Server –
Related- DHCP Snooping
Steps of DORA process in DHCP:
Now let’s take a look at what happens when these messages are exchanged between DHCP Client and DHCP Server.
Two 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.
STEP 1: DHCP DISCOVER
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.
STEP 2: DHCP OFFER
DHCP server receives the DHCP discover a message from the 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.
STEP 3: DHCP REQUEST
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.
STEP4: DHCP ACK
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 –
Hope you would have understood the DHCP Dora Process. Read our other blogs for more information – >> What is NIC? >> DHCP vs RARP
FAQs Related to DORA Process:
Hope you would have understood the DHCP Dora Process. Read our other blogs for more information –
>> What is NIC?
>> DHCP vs RARP