Dynamic DNS is a system which allows the domain name data held in a name server to be updated in real time. The most common use for this is in allowing an Internet domain name?to be assigned to a computer with a varying (dynamic) IP address. This makes it possible for other sites on the Internet to establish connections to the machine without needing to track the IP address themselves. A common use is for running server software on a computer that has a dynamic IP address, as is the case with many consumer Interent service providers.
To implement dynamic DNS it is necessary to set the maximum caching time of the domain to an unusually short period (typically a few minutes). This prevents other nodes on the Internet from retaining the old address in their DNS cache, so that they will typically contact the name server of the domain for each new connection.
Dynamic DNS is an integral part of Active Directory, due in part to the fact that domain controllers register their service records (a category of data in the Internet Domain Name System specifying information on available services.) in DNS so that other computers in the Domain (or Forest) can find them.---by http://en.wikipedia.org