Incremental Zone Transfer

As we said earlier in the chapter, one of the problems the old DNS had was that anytime a database needed to be updated, the name server that received the update received a lot of information it already had. That was a large waste of bandwidth and time. In dynamic DNS, the database is going to be changing frequently. Therefore, the problems would have gotten worse, not better.

To reduce this latency in sending out the changes to a DNS database, there is now a way that actively notifies name servers of the change. This is accomplished by the NOTIFY extension of the DNS. The NOTIFY packet, which is sent by a Master server, does not contain any zone changes information. It merely notifies the other servers that some changes have been made to a zone and that a zone transfer needs to be initiated. When the zone transfer is initiated, it can be an incremental transfer (IXFR), which is more efficient. It transfers only the changed portion(s) of the zone.

The IXFR protocol is defined in RFC 1995.

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