QUICK TIP - DORA Process – 1 Hot Basic Interview Question

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DHCP DORA Process- Hot! 1 Basic Interview Questions need to Attention – DHCP stands for Dynamic Host Configuration Protocol. Thus, DHCP used to provide IP addresses to different Hosts or Client machines present in a Network. DORA is nothing but a sequence of messages which is exchanged between the DHCP Server and Client.

Introduction – DHCP DORA Process

DORA stands for mentioned messages :

  • Discover
  • Offer
  • Request
  • Acknowledgement

Now, we will take a look at exactly what happens when DHCP client requests an IP address from DHCP Server.  There are some messages which are exchanged between the DHCP Server and Client. These messages are explained below.

Keypoint: All DHCP Messages are broadcast at Network Layer (i.e Layer 3).

Now, take a look on this image. This image will clear the sequence of different messages which is used in DORA Process.

DHCP DORA Process

DHCP Discover Message – DORA

Discover Message is the first message of the DORA process. In this message, the DHCP client wants to discover a DHCP Server and hence sends a DHCP Discover message. Different fields of Discover message are :

Source IP: 0.0.0.0

Destination IP: 255.255.255.255

Source MAC: DHCP Client Machine MAC Address

Destination MAC: FF:FF:FF:FF:FF:FF

Hence, we can say that the DHCP Discover message in DORA process always broadcast at the network and data link layer.

DHCP Offer Message – DORA

As soon as DHCP Server receives Client Discover message, the DHCP server reply to DHCP client as an offer message.

Source IP: DHCP Server IP Address

Destination IP: 255.255.255.255

Source MAC: DHCP Server Machine MAC Address

Destination MAC: DHCP client MAC Address

Now, as you can see, still the Destination IP address in the DHCP Offer Message header has a broadcast IP address. This is because the client didn’t get an IP address from DHCP Server. But, this time, this message is broadcast at Network Layer only.

DHCP Request Message

Now, the DHCP client machine receives the DHCP Offer message and replies with a DHCP request message. This message basically tells the DHCP server that I’m fine with this IP address. Please allocate this IP address to me. The DHCP Request Message header has the following main fields:

Source IP: 0.0.0.0

Destination IP: 255.255.255.255

Source MAC: DHCP Client Machine MAC Address

Destination MAC: DHCP Server MAC Address

Now, as you can see, still Client Source IP address is 0.0.0.0. This is because the client still didn’t get an IP address from DHCP Server. Also, this message has broadcast only at the network layer of the OSI Model.

DHCP Acknowledgement Message

DHCP acknowledge message is the last message of the DORA process. It is sent by the DHCP Server to DHCP Client. This message is a reply to the DHCP Request message. This message header has the following main fields:

Source IP: DHCP Server IP Address

Destination IP: 255.255.255.255

Source MAC: DHCP Server Machine MAC Address

Destination MAC: DHCP client MAC Address

After this message, the DHCP client will get an IP address. This message has broadcast at the network layer but unicast on the Data Link layer.

Easy to understand and memorise

This step we can help you to summarise to easily understand and memorise. You just remember there are four main steps in DORA. Therefore, you can imagine like you are shopping.

Base on “D“, you will know the first step is DISCOVERED message like you call shopper to buy something.

Then, “O” is OFFERED message like the shopper ask you what you want to buy.

Next, “R” is RESPONSE message that you answer what you want to buy.

Finally, “A” is ACKNOWLEDGED message that the shopper will give you what you want.

 

Conclusion

The process of requesting an IP address from DHCP client to DHCP server is simple and easy to remember. Moreover, DORA is a standard that many router following the process and basic knowledge in Networking area.

This is the reason why, you should know about this because it is very useful for you in many situations such as troubleshooting your router, client DHCP, server DHCP and answering interview question. We added some popular questions on our website that you can meet these during your interview.

DORA process
Summarise the process

 

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How many percentages that you will meet the question in your interview?
60%
High frequency rate
  • Possibility 80%
  • Difficulty Level 40%
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