How Active Directory Dynamic DNS updates works behind the scenes?

Solution 1:

By default the client itself does its own DDNS update if it is XP or newer. A DHCP server can perform proxy updates for DNS clients that don't support updating their own client records.

You can also force a client registration via ipconfig /registerdns

Here's a good link, simple enough: http://technet.microsoft.com/en-us/library/cc771255.aspx

Domain Name System (DNS) client computers can use dynamic update to register and dynamically update their resource records with a DNS server whenever changes occur. This reduces the need for manual administration of zone records, especially for clients that frequently move or change locations and use Dynamic Host Configuration Protocol (DHCP) to obtain an IP address.

Solution 2:

From what I understand, MS clients can update their resource records (Understanding Dynamic Update) via secure, AD integrated updates.

Also, MS DHCP can do this on behalf of a client (e.g. non-MS devices). This requires non-secure updates, IIRC.