Distributed Name Service (DNS) Management Operations Manual

DNS Database Replication
How DNS Exports the Name Database
31258 Tandem Computers Incorporated 5–7
Although you can request updates to a name from any node where DNS is installed,
DNS actually accomplishes and propagates the updates through the definition node
for that name. Names preferably should be defined on the nodes where the objects
physically exist, although DNS does not enforce this.
For more information about the COPY command, see “Updating Definitions on
Unavailable Nodes” in Section 3 and the COPY command description in Section 7.
Type Mismatch and Hold
Queues
Type mismatches may occur in two different cases:
As the result of the exporter attempting to process a secondary queue request.
This is the normal case.
If the importing node has been reinitialized and the exporting node is attempting
to re-export all names defined on the exporting node. (The names defined on the
exporting node were replicated on the importing node prior to its being
reinitialized.)
DNS treats these two cases differently. Mismatches occurring in the first case cause
the name exporter to remove the request from the secondary queue and place it in a
hold queue. The name exporter proceeds to process the next request in the remote
system’s secondary queue.
Mismatches occurring in the second case cause export to the remote system to be
disabled.
In both cases, you must take the steps necessary to correct the problem and then issue
an ENABLE EXPORT command. This command, in addition to enabling export (if it is
currently disabled), causes the exporter to attempt reprocessing of all entries currently
in the hold queue for the system specified in the ENABLE EXPORT command.
How DNS Avoids Name
Duplication and
Incompatibility
When a new name is defined at its definition node, the systems in the name’s domain
are not consulted. Consequently, there is a possibility that the new name duplicates an
existing name defined on another node in the new name’s domain. To avoid such
name duplications, each DNS name is qualified by the name of its definition node. For
example, if the name LINE46 is defined on system \NEWYORK, the fully qualified
form of that name is LINE46 ON \NEWYORK. This fully qualified form need only be
used, however, on nodes where more than one LINE46 is known, such as LINE46 ON
\NEWYORK and LINE46 ON \CHICAGO. For more information on unique names,
see “Uniqueness of Names: Parts of a DNS Name” in Section 4.