NAMED is the DNS name server in BS2000. NAMED enables both recursive and iterative queries as well as caching and can be optionally configured as:
a master server,
a slave server,
a "caching-only" server,
a forwarding server.
Recursive and iterative queries
On receiving a query of another name server or the resolver, NAMED first tries to answer the query on the basis of its own database.
If this does not succeed, NAMED behaves as described below, depending on the configuration:
recursive queries (default case)
In the case of a recursive query, the name server performs all activities required to answer that query. Here recursive means that the name server repeats the same basic procedure (sending queries to a remote name server and following links) until it receives the answer it is looking for.
The resolver sends a recursive query to a name server to obtain information on a particular domain name. The name server should then supply the requested data or return an error message reporting that
the data of the requested type is not available or
the specified domain name does not exist.
With a recursive query the name server cannot simply refer the resolver to another name server but must itself contact the next name server it knows.
iterative queries
The name server rejects a query if it cannot be answered locally, i.e. with information from its own database. The source of the query must then use some other name server to get an answer for the query.
Caching
NAMED stores all incoming information during the iterative process in a local cache, which extends the database and reduces the answering time. If too many queries are required, the cache can grow very large.
Master server and slave server
DNS name servers administer zones, if they are authoritative for the zone. As a rule, the DNS within a zone is not implemented on a single NAMED server, but on a group of such servers. To enable failover security, apart from the master server (primary server), at least one additional server should be set up as a slave server (secondary server), which manages a copy of the master server data. NAMED can be configured both as a master server and as a slave server.
Changes in the zone data are always made on the master server. The Master name server for a zone reads the zone data from a file on its host, the zone data file. The slave server, which always receives its data only from the master server, queries the master server periodically to check whether its own copy of the master server data needs to be updated. The transfer of master server data to the slave server is known as a zone transfer.
If desired, the master server can also be configured to actively notify all slave servers when the zone data is changed. These slave servers can then initiate the zone transfer. A slave server that only takes over NS Resource Records from the master server is known as a stub server.
During a zone transfer, the slave servers can save the transferred data to backup files. If the backup files are not available on starting up a slave server, the slave server in question requests the current data from the master server.
Zone data should be transferred regularly even if it has not been modified. This enables the data to be accessed even if the master server is not available.
A NAMED server may be used in different zones as a master and/or slave server.
Forwarding servers and forwarders
If NAMED is configured as a forwarding server, it forwards all queries that it cannot answer with its own database to special name servers (called "forwarders") for recursive processing. These forwarders then try to obtain the required answers in an iterative process. If the forwarders cannot return the final information, the forwarding server will try to independently answer the query again, depending on its configuration, or simply abort the process.
Forwarding-only mode
In this mode a name server that uses a forwarder does not inquire at other name servers if the forwarder supplies no result.
Caching-only servers
NAMED can also be configured as a "caching-only" server. A caching-only server does not maintain its own committed database, but requests information from other authorized name servers. This information is then saved in the cache of the caching-only server.
Views
The view statement enables a NAMED server to be configured in such a way that it handles queries differently depending on the sender address.