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Unformatted text preview: m into physical disk partitions. Just as we can't tell from Figure 14.1 where the zones of
authority lie, we can't tell from a similar picture of a Unix filesystem which directories are on which disk partitions.
Once the authority for a zone is delegated, it is up to the person responsible for the zone to provide multiple name
servers for that zone. Whenever a new system is installed in a zone, the DNS administrator for the zone allocates a
name and an IP address for the new system and enters these into the name server's database. This is where the need for
delegation becomes obvious. At a small university, for example, one person could do this each time a new system was
added, but in a large university the responsibility would have to be delegated (probably by departments), since one
person couldn't keep up with the work.
A name server is said to have authority for one zone or multiple zones. The person responsible for a zone must provide
a primary name server for that zone and one or more secondary name servers. The primary and secondaries must be
independent and redundant servers so that availability of name service for the zone isn't affected by a single point of
The main difference between a primary and secondary is that the primary loads all the information for the zone from
disk files, while the secondaries obtain all the information from the primary. When a secondary obtains the information
from its primary we call this a zone transfer.
When a new host is added to a zone, the administrator adds the appropriate information (name and IP address
minimally) to a disk file on the system running the primary. The primary name server is then notified to reread its
configuration files. The secondaries query the primary on a regular basis (normally every 3 hours) and if the primary
contains newer data, the secondary obtains the new data using a zone transfer.
What does a name server do when it doesn't contain the information requested? It must contact another name server.
(This is the distributed nature of the DNS.) Not eve...
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- Spring '12