The DHCP Message Format
The DHCP message format is similar to that of BOOTP message format. That is why DHCP is backward compatible with BOOTP.
Figure 14.6 shows the structure of a DHCP message.
Figure 14.6. The DHCP message format differs from the BOOTP message format only in the 16-bit FLAGS field.
The DHCP message format also has a 16-bit FLAGS field and extra subfields in the Options field. The FLAGS field forces the client to broadcast its reply to the client. A unicasted reply cannot be processed by the client because it does not identify its own IP address.
The Options field has additional subfields, such as a field that specifies ...
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