For our example, the client and server are connected through an Ethernet connection. Each protocols are assigned a unique identifier which is found in this table. ![]() Some examples of layer 2 (the data link layer) protocols includes Ethernet and 802.11x. Hardware Type (8 bits) - this field indicates the type of Layer 2 protocol that is using the DHCP. For example, if we examine the OP Code of a DHCP Discover, we will find 0x01 in this field whereas we will find 0x02 if we examine a DHCP Acknowledge packet. The value 0x01 represents request, while 0x02 represents response. In DORA, the Discover and the Request are consider as request packet meanwhile, the Offer and Acknowledge are consider as response packet. OP Code (8 bits)- this field indicates whether this DHCP packet is a request or a response packet. Note: in Wireshark, type ‘bootp’ in the filter bar to show only DHCP packets. The packet capture file (.pcap) of DORA can be downloaded here for your own experiment. The DORA messages are captured using Wireshark (a popular network sniffer). We sniff the network when the end point is asking for a dynamic IP. There are two end points one being the DHCP client, and one being the DHCP server. Here, we explain the DHCP DORA using the packets obtained from this network (shown below). But how does the DHCP client and DHCP server knows who is asking for an IP? Who is the server in the LAN? What’s IP is being offered by the server? and whether the client accept the IP address that is being offered? Well, simply because any hosts that support TCP/IP understand DHCP - and that’s where all the magic lies in the packet header of DHCP packets from DORA. We have learnt the intuition behind each messages in DORA and that network hosts can automatically obtained an IP by completing DORA process. DHCP use (D)iscover, (R)equest, (O)ffer and (A)cknowledge to assign dynamic IP to network hosts. If you would like to learn how DHCP works in the eyes of human, read here instead. Specifically, we will go deep and analyse 4 types of DHCP packets from DORA using Wireshark. In this story, we will demonstrate how DHCP works in the eyes of the machines.
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