Problem related with dhcp Client packet

Hi,
We are trying to update the DNS Records from dhcp server. That is we
need to support ddns update from dhcp server. For this we are forming
dhcp client packet format where we need to set the option 61 "Client
identifier". We have tried to make the format for "Client identifier"
where we need to make the format for "Hardware type and Client MAC
Address". It would be great, if you can give some information for
formating this packet.

Thanks in Advance.
Regards,
Agnibhu.