Technical data

8.7 BIND Server Functions
If a network consists of relatively few hosts, host name to IP address translations
can be accomplished by using a centralized hosts database file.
As soon as a network connects to another network, or when the number of hosts
grows large, a more robust method for performing host name/IP address translation
is required. In particular, when a network is part of the worldwide internet, no
single database can keep track of all addressing information. A considerable
number of hosts and network domains are added, changed, and deleted every day.
BIND uses different types of name servers to ensure that all queries are resolved
quickly and efficiently:
•Rootservers
• Master name servers
•Slavenameservers
• Forwarder servers
• Caching-only servers
When a client makes a query, a name server can be in one of three possible states:
• It knows the IP address authoritatively, based on addresses residing in its
data files.
• It knows the IP address but not authoritatively, from data cached in its memory
from a previous query
• It does not know the address and must refer the query to another server.
The following sections discuss the different types of name servers and their
primary responsibilities in the distributed environment of BIND and DNS.
8.7.1 Root Name Servers
Root name servers are the master name servers for the top-level domains of the
internet root zone. If the root name server is not the authority for a zone, it knows
whom to contact to find out which server is the authority.
If a nonroot server receives a request for a name that is not within its zone, the
server starts name resolution at the root zone and accesses the root servers to get
the needed information.
The InterNIC determines root servers for the top-level domain, such
as A.ROOT_SERVERS.NET, which is a current server name (formerly,
ns.internic.net
). These servers change from time to time. You can obtain
the up-to-date list by:
• Copying the named root file maintained at the InterNIC by using FTP
anonymous login to
ftp.rs.internic.net
(198.41.0.6). The file is in the
domain subdirectory.
•Usingthe
dig
utility.
• Using the online registration process at the InterNIC web site.
These servers know about all the top-level DNS domains on the Internet. You
must know about these servers when you make queries about hosts outside of
your local domain. The host names and internet addresses of these machines
change periodically. Therefore, check with the InterNIC to obtain changes, and
store them in the hints file of the BIND name servers (usually called
ROOT.HINT
on a TCP/IP Services system).
Domain Name System/BIND (DNS/BIND) 8–5