Technical data

8.7.6 Configurations Without Internet Access
You can run the BIND service on a local network that does not have internet
access. In this configuration, the servers resolve local queries only. Any request
that depends on Internet access goes unresolved.
8.7.7 Zone Transfers
Zone transfers are the process by which slave servers obtain their zone data. When
a slave server starts up and periodically thereafter, the server checks whether its
data is up to date. It does this by polling a master server to see whether the master
server’s zone database serial number is greater than the slave’s. If so, the slave
performs a zone transfer over the network.
An essential point in this polling environment is that whenever a change is made to
a master server’s zone database file, the zone’s serial number must be incremented
for the change to propagate to other servers. If the serial number does not change,
the slave server does not know it should perform a zone transfer.
Zone Change Notification
In addition to slave servers polling to determine the necessity for a zone transfer,
BIND provides a mechanism for a master server to notify slaves of changes to
a zone’s database.
When a master server determines that a change has been made to a database, it
will send a NOTIFY message to all the slave servers for the zone. The slave servers
respond with a NOTIFY response to stop any further NOTIFY messages from the
master before they query the master server for the start of authority (SOA)
record of the zone. When the query is answered, the slave checks the serial number
in the SOA record and if the serial number changes, the slave transfers the zone.
This interrupt feature combined with polling provides a good balance between slow
propagation of data because of long refresh times and periods of inconsistent data
between authority servers when zone data is updated.
Dynamic Update
DNS Dynamic Update, a BIND feature, provides for zone changes in real time,
without having to change a database file and then signal the master server
to reload the zone data. Most often, these changes come from other network
applications, like DHCP servers, which automatically assign an IP address to a
host and then want to register the host name and IP address with BIND.
Dynamic Update provides for:
• Adding and deleting individual resource records
• Deleting a set of resource records with the same name, class, and type
• Deleting all records associated with a given name
• Specifying that prerequisite records exist before adding an address record
Dynamic updates are remembered over system reboots or restart of the BIND
server. Whenever the BIND server starts up, it looks for and reads the file where it
logged updates (typically,
domain.db_jnl
) and merges the updates into its cache
of zone data. While running, the BIND server occasionally writes any pending
dynamic updates to the zone database file.
Domain Name System/BIND (DNS/BIND) 8–7