DNS

The Domain Name System. This is an Internet standard that maps human readable names to Internet Protocol
addresses. This standard is introduced in RFC 1034 with implementation details provided in RFC 1035. 
The standard is based on a distributed database with an relational tree structure.

UDNS

Universal DNS.

BIND

The Berkeley Internet Name Domain. This is an Open Source implementation of the DNS standard developed
by the ISC. Details can be found at http://www.isc.org/products/BIND.

ISC

The Internet Software Consortium is a non-profit organization that develops and maintains Open Source
applications for the Internet. More information can be found at http://www.isc.org.

Domain Name

A name identifying a single node in the DNS tree structure. When addressing a particular node in the tree,
each name is separated with a period with the lowest addressed node (leaf node) listed first and each parent
node in subsequent order. A host called "www" in the Qwest production network would have the
domain name, "www.qwest.net".

Domain Name Space

The superset of all domain names in the Domain Name System.

Domain

A domain is a subset of the domain name space that consists of a specific node and all child nodes
below it in the tree.

subdomain

This term refers to a subset of another domain, i.e. a domain name, with a parent, that identifies
a set of nodes consisting of itself and all child nodes below it.

root domain

The root node of the DNS tree has no name, and is signified with a single period.

FQDN

A Fully Qualified Domain Name explicitly identifies a specific node in the DNS tree.
It consists of the set of all domain names for all parent nodes in the tree up to the root
node and therefore is a domain name that ends with a period.

Host Name

This is a domain name that identifies a specific network interface on an Internet-connected machine.
A domain name can identify both a domain and a host.

Top-level Domain

A domain that has the root domain as its parent.

Second-level Domain

A domain that has a top-level domain as its parent.

Root Servers

The Top-Level Domains are maintained by a set of name servers which in turn are maintained by a
coalition of non-profit organizations, academic institutions, and commercial network providers. These
servers are the starting point for a search of the domain name system. They maintain the registrations
of all the authoritative servers for the second-level domains.

Forward lookup

A query of the Domain Name System that resolves a domain name to an address.

Reverse lookup

A query of the Domain Name System that resolves an address to a domain name. This is done via the
‘ARPA’ top-level domain. The second-level domain for Internet addresses is called ‘inaddr’. The subdomains
of ‘in-addr’ domain consist of the octets for IP addresses in reverse order with the high order octets higher
in the tree than the low order octets. For example the IP Address "10.1.2.3" would have a reverse domain name
mapping with the FQDN "3.2.1.10.in-addr.arpa.".

Zone

The unit of organization of the Domain Name Space. A zone is identified by a SOA (Start Of Authority)
record. It consists of the subset of a domain that contains all domain names below the domain name of the
SOA record that are associated with that SOA, i.e. sub-domain-names that are not associated with their own,
separate SOA record. A zone may contain the entire domain set, or any subset thereof.

Zone File

Typically, an implementation of the Domain Name System maintains the persistency of a zone as a file
on the name server that is the origin of the zone, as specified by the SOA record.

Name Server

A server node on the network running an application that provides the DNS service. This service is
provided on the well known Internet port 53.

Primary/Master Name Server

A name server that maintains a zone. This server typically provides DNS service for the zone. This
is the source of origin for the zone. This server provides the persistence of the zone.

Secondary/Slave Name Server

A name server that provides DNS service for a given zone that is not maintained by the server, but
is instead transferred via the DNS protocol from a Primary/Master Name Server. This provides redundant
service for the zone.

Authoritative Name Server

A name server that provides DNS service for one or more domains. Such a server is the authoritative
server for each domain it services. For each domain, the authoritative server is registered with parent
domain as authoritative for the domain. Every domain must have two or more registered name servers that
can provide authoritative DNS service for it. An authoritative name server may be authoritative for a
domain and a subset of any number of its subdomains.

Delegation

A name server for a parent domain that has a subdomain maintained by a separate set of name servers
refers all queries for the subdomain to those name servers, in other words it delegates authority for the
subdomain to a separate set of servers.

Hidden Primary

A Primary/Master Name Server may have two or more Secondary/Slave servers that are registered as
authoritative for the domains it maintains, while it remains unregistered. This is a security measure
used to hide the actual source of origin for a zone from the Internet community. The SOA record for the
zone can list one of the Secondary/Slave servers as the origin of the zone in order to insure that the
actual Primary/Master remains undetected.

RR

A zone consists of RR’s (Resource Records) as the unit of data used to resolve a name. A resource
record provides the data for a response to a DNS query for a given domain name.

RR Type

There are several different types of data that can be associated with a domain name.
The type of data returned by a given RR is specified by its type. The following types are significant
to this specification:


A - Address – a 32 bit IP Address
CNAME - Canonical Name – a domain-name which specifies the primary name for the owner. A name that
resolves to this type is an alias.
HINFO - Host Information – specifies the CPU and OS type for the named host.
LOC- Location - Used to describes the physical geographical location of the host.
MX - Mail Exchanger – a domain-name that identifies a host willing to act as the mail exchanger for
the given domain along with the preference for this record among others for the same name.
NS - Name Server – a domain name that identifies a host that should be authoritative for the given
domain.
PTR - Pointer – a domain-name that refers to another name in the domain-name space. This is usually
applied to resolve reverse lookups.
SOA - Start of Authority - designates the start of a zone and provides zone parameters
TXT – Text – a text record associated to a domain-name that can be accessed via a query.
WKS - Well Known Services - used to list well known services provided by a domain-name
(i.e. TELNET, FTP, SMTP, TIME)

Query Type (qtype)

There are different types of queries supported by DNS in order to support the different
types of RR’s. The query types are a super set of the RR Types. In addition to the above listed RR Types,
this specification is concerned with the following additional query types:


AXFR – A request to transfer an entire zone.
IXFR – A request to transfer only an incremental portion of a zone. This results in only the changed
portion of the zone being transferred.
* (or ALL) – A request to transfer all RR’s associated with the given domain name.

Host Resolver

The client side executable library that manages the resolution of a domain name in the domain name
system for applications on the host.

Recursive Query

A host resolver resolves a domain name by sending an appropriate DNS query to a known name server
(as specified in the DNS configuration for the host). The query specifies that recursion is desired.
The known name server then recursively searches the Domain Name Space tree until an authoritative answer
for the given domain name is received. The name server begins with the root node resulting in a query to
the root servers for the top-level domain of the given domain name. At each node in the tree the
authoritative server for that domain refers the querying name server to authoritative name servers for the 
next node (domain name) listed in the FQDN for the queried domain name. This process continues until querying
name server receives an authoritative answer, which it then provides in the response to the host resolver.
Typically the resolving name server, then caches the information it collects as it recursively searches
the Domain Name Space. The next query that requires any information that it has already collected can then
be more efficiently processed. A recursive query results in one definitive answer requiring the queried
name server to issue consecutive queries until the answer can be provided. Host resolver queries
are recursive.

Iterative Query

A query that does not specify that recursion is desired is an iterative query. The answer to an
iterative may be a definitive answer or a referral to the next authoritative name server in the tree.
The queried name server always responds with an answer from the data it maintains locally without searching
the Domain Name Space. Queries issued by name servers are iterative queries.

Authoritative Answer

This is an answer that resolves a domain-name from zone data maintained by a name server that is either
a master or a slave for the zone.

Non-authoritative Answer

This is an answer that resolves a domain name from cached data by a name server that is not
authoritative for the domain.

IETF

The Internet Engineering Task Force. More information can be found at http://www.ietf.org.

RFC

A Request For Comments. This is the documentation format for Internet standards.
The conventions for this documentation can be found in rfc0024. More information can be found at
http://www.ietf.org.