Information Technology Reference
In-Depth Information
Zone transfers occur in one of two ways: full zone transfers (AXFR) and incremental
zone transfers (IXFR) .
When a new secondary server is configured for the first time, it receives a full
zone transfer from the primary DNS server. The full zone transfer contains all of the
information in the DNS database. Some DNS implementations always receive full zone
transfers.
After the secondary server receives its first full zone transfer, subsequent zone transfers
are incremental. The primary name server compares its zone version number with that of
the secondary server, and it sends only the changes that have been made in the interim.
This significantly reduces network traffic generated by zone transfers.
The secondary server typically initiates zone transfers when the refresh interval time
for the zone expires or when the secondary or stub server boots. Alternatively, you can
configure notify lists on the primary server that send a message to the secondary or stub
servers whenever any changes to the zone database occur.
When you consider your DNS strategy, you must carefully consider the layout of your
network. If you have a single domain with offices in separate cities, you want to reduce the
number of zone transfers across the potentially slow or expensive WAN links, although this
is becoming less of a concern because of continuous increases in bandwidth.
Active Directory Integrated zones do away with traditional zone transfers altogether.
Instead, they replicate across Active Directory with all of the other AD information. This
replication is secure and encrypted because it uses the Active Directory security.
How DNS Notify Works
Windows Server 2012 R2 supports DNS Notify. DNS Notify is a mechanism that allows
the process of initiating notifications to secondary servers when zone changes occur (RFC
1996). DNS Notify uses a push mechanism for communicating to a select set of secondary
zone servers when their zone information is updated. (DNS Notify does not allow you to
configure a notify list for a stub zone.)
After being notified of the changes, secondary servers can then start a pull zone transfer
and update their local copies of the database.
Many different mechanisms use the push/pull relationship. Normally, one
object pushes information to another, and the second object pulls the
information from the first. Most applications push replication on a change
value and pull it on a time value. For example, a system can push replica-
tion after 10 updates, or it can be pulled every 30 minutes.
To configure the DNS Notify process, you create a list of secondary servers to notify.
List the IP address of the server in the primary master's Notify dialog box (see Figure 2.8).
The Notify dialog box is located under the Zone Transfers tab, which is located in the zone
Properties dialog box (see Figure 2.9).
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