I downloaded and installed ppp-dhcp plugin for my ppp server and
wondering if you can help me with my problem.

With the plugin, the ppp client is able to obtain an IP address from a
dhcp server. However I notice that its IP address is the same as ppp
server's IP address. By looking at the dhcp message, it seems that it
lists ppp server's mac address as the client MAC address, therefore the
dhcp server returns the same IP address which is passed to the client.

How can I make the dhcp server turns dynamic IP address to the client?

Thanks in advance.