"The Domain Name System was originally designed to support queries of a statically configured database. While the data was expected to change, the frequency of those changes was expected to be fairly low, and all updates were made as external edits to a zone's Master File.
Using this specification of the UPDATE opcode, it is possible to add or delete RRs or RRsets from a specified zone. Prerequisites are specified separately from update operations, and can specify a dependency upon either the previous existence or nonexistence of an RRset, or the existence of a single RR.
UPDATE is atomic, i.e., all prerequisites must be satisfied or else no update operations will take place. There are no data dependent error conditions defined after the prerequisites have been met.”
关于DNS设置，看看这篇文章：http://blog.csdn.net/orapeasant/archive/2007/09/26/1801437.aspx
How To Configure Dynamic DNS (Fedora Core 4 Setup)
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This document [RFC3007] defines a means to secure dynamic updates of the Domain Name System (DNS), allowing only authorized sources to make changes to a zone's contents. The existing unsecured dynamic update operations form the basis for this work.
Familiarity with the DNS system [RFC1034, RFC1035] and dynamic update [RFC2136] is helpful and is assumed by this document. In addition, knowledge of DNS security extensions [RFC2535], SIG(0) transaction security [RFC2535, RFC2931], and TSIG transaction security [RFC2845] is recommended.
This document updates portions of RFC 2535, in particular section 3.1.2, and RFC 2136. This document obsoletes RFC 2137, an alternate proposal for secure dynamic update, due to implementation experience.