Comprehension question to DDNS

[Markus Feldmann]

Hi All,

since about 1 year i got my DNS and DHCP to work but not DDNS. So i can 
only work with static IP's.

Does my DHCP-Server request and DDNS-Update automatically, when a client 
  gets an IP from the DHCP-Server.

Or:

Does the client ask the DHCP-Server for an IP and after he got one he 
request a DDNS-Update by himself?

If the second case is right, then how do i have to configure my Linux 
client?

The DNS Server-System does not record any DDNS-Update request, so i 
think he will not be asked???

Help!!! :-)

Regards Markus