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DHCP for Windows 2000 by Neall Alcott

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Dynamic Update

It is important to remember that the entire basis of DNS was rooted in the HOSTS file—a static text file. As such, DNS has traditionally been maintained manually by a network administrator. The administrator made edits to the zone file by hand.

However, with the advent of DHCP and dynamic IP addressing, the operation of manually updating the DNS database quickly became inefficient and unmanageable. Since an administrator could not possibly process the number of updates required, many organizations became very selective towards DNS updates. Only important devices, such as servers, network printers, routers, etc. would be assigned hostnames and added to the DNS database.

To handle the overburdening load of DNS updates, the IETF released RFC2136, “Dynamic Updates in DNS (DNS UPDATE).” This RFC defined a new DNS message type called UPDATE. The UPDATE message is used to define and remove resource records from a designated zone. It also has the ability to perform tests to determine if a particular resource record currently exists in the DNS database.

Since changes can only occur on the primary name server for a zone, the RFC also specified that if a secondary server receives an UPDATE message, it must forward the UPDATE request to the primary name server. Of course, with an Active Directory-integrated DNS database, all updates are processed by a domain controller.

Another concern is zone transfers. During zone transfers, the zone file is locked while the secondary server ...

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