Technical data

8.7.2 Master Name Server
There are two types of master servers: a master name server and a slave name
server (also called a secondary master name server).
The master server is the primary authority for the zone. The master server has
complete information about the zone, and it stores the information in its database
files. If network information changes, those changes are captured in the master
server’s database files.
A server can be a master server for more than one zone, acting as the master name
server for some zones and a slave name server for others.
You can have more than one master server; however, maintaining two sets of
database files requires making the same changes to both sets of files. A more
efficient solution is to have one master server and one or more slave servers that
obtain their zone information from the master server.
8.7.3 Slave Name Server
A slave name server is an administrative convenience that provides redundancy
of information and that shares the load of the master name server. A slave name
server receives its authority and zone data from a master name server. Once it is
running, a slave name server periodically checks with the master name server for
zone changes. If the slave’s serial number is less than the master’s serial number,
the slave requests a zone transfer.
The slave name servers poll the master server at predetermined intervals specified
in the zone database files. A time lapse between changing the master server’s
databases and the slave name servers requesting the update may exist.
8.7.4 Forwarder Servers
Often it is beneficial to limit the traffic to the Internet. The reason might be a slow
internet connection or you are being charged by the number of packets.
Funneling DNS Internet queries through one name server can reduce the number
of queries going out to the Internet. A name server that performs this function is a
forwarder. The forwarder handles all off-site queries and in doing so builds up
a cache of information; this reduces the number of queries that the forwarder
needstomaketosatisfyaquery.
Forwarder servers have access to the Internet and are able to obtain information
regarding other servers that is not currently found in local caches. Because a
forwarder server can receive requests from several slave servers, it can acquire
a larger local cache than can a slave server. All hosts in the domain have more
information available locally because the forwarder servers have a large cache.
This means that the server sends fewer queries from that site to root servers on
networks outside the internet.
8.7.5 Caching-Only Servers
All servers cache the information they receive for use until the data expires. The
length of time a server caches the information is based on a time-to-live (TTL) field
attached to the data the server receives.
Caching-only servers have no authority for any zone, and thus do not have
complete information for any zone. Their database contains information acquired
in the process of finding answers to clients’ queries.
8–6 Domain Name System/BIND (DNS/BIND)