DNS terms and definitions

Terms and Definitions

The following are some important DNS-related terms.

Authoritative DNS server A DNS server that hosts a primary or secondary copy of zone data. Each zone has at least one authoritative DNS server.

Conditional forwarding A DNS query setting that enables a DNS server to route a request for a particular name to another DNS server by specifying a name and IP address. For example, a DNS server in chicagotech.net can be configured to forward queries for names in ms-mvps.com to a DNS server hosting the ms-mvps.com zone.

Delegation The process of using resource records to provide pointers from parent zones to child zones in a namespace hierarchy. This enable DNS servers in a parent zone to route queries to DNS servers in a child zone for names within their branch of the DNS namespace. Each delegation corresponds to at least one zone.

DNS client resolver A service that runs on client computers and sends DNS queries to a DNS server. Some resolvers use a cache to improve name resolution performance.

DNS namespace The hierarchical naming structure of the domain tree. Each domain label that is used in a fully qualified domain name (FQDN) indicates a node or branch in the domain tree. For example, ms-mvps.chicagotech.net is an FQDN that represents the node ms-mvps, under the node chicagotech, under the node net, under the DNS root.

DNS server A computer that hosts DNS zone data, resolves DNS queries, and caches the query responses.

Domain tree In DNS, the inverted hierarchical tree structure that is used to index domain names within a namespace. Domain trees are similar in purpose and concept to the directory trees used by computer filing systems for disk storage.

Public namespace A namespace on the Internet, such as www.ms-mvps.com, that can be accessed by any connected device. Beneath the top-level domains, the Internet Corporation for Assigned Names and Numbers (ICANN), the Internet Assigned Numbers Authority (IANA), and other Internet naming authorities delegate domains to organizations such as Internet Service Providers (ISPs), which in turn delegate subdomains to their customers or host zones for their customers.

Forward lookup zone An authoritative DNS zone that is primarily used to resolve network resource names to IP addresses.

Fully qualified domain name (FQDN) A DNS name that uniquely identifies a node in a DNS namespace. The FQDN of a computer is a concatenation of the computer name (for example, ms-mvps) and the primary DNS suffix of the computer (for example, chicagotech.net), and a terminating dot (for example, chicagotech.net.).

Internal namespace A namespace internal to an organization to which it can control access. Organizations can use the internal namespace, for example chicagotech.local to shield the names and IP addresses of its internal computers from the Internet. A single organization might have multiple internal namespaces. Organizations can create their own root servers and any subdomains as needed. The internal namespace can coexist with an external namespace.

Iterative query A query made by a client to a DNS server for an authoritative answer that can be provided by the server without generating additional server-side queries to other DNS servers.

Primary DNS server A DNS server that hosts read-write copies of zone data, has a DNS database of resource records, and resolves DNS queries.

Secondary DNS server A DNS server that hosts a read-only copy of zone data. A secondary DNS server periodically checks for changes made to the zone on its configured primary DNS server, and performs full or incremental zone transfers, as needed.

Recursive query A query made by either a client or a DNS server on behalf of a client, the response to which can be an authoritative answer or a referral to another server. Recursive queries continue until the DNS server receives an authoritative answer for the queried name. By default, recursion is enabled for Windows Server 2003 DNS.

Resource record (RR) A DNS database structure containing name information for a particular zone. For example, an address (A) resource record can map the IP address 10.0.0.2 to the name ms-mvps.chicagotech.net or a namespace (NS) resource record can map the name chicagotech.net to the server name DNS1.contoso.com.

Reverse lookup zone An authoritative DNS zone that is primarily used to resolve IP addresses to network resource names.

Stub zone A partial copy of a zone that can be hosted by a DNS server and used to resolve recursive or iterative queries. Stub zones contain the Start of Authority (SOA) resource records of the zone, the DNS resource records that list the zone’s authoritative servers, and the glue address (A) resource records that are required for contacting the zone’s authoritative servers. Stub zones are used to reduce the number of DNS queries on a network, and to decrease the network load on the primary DNS servers hosting a particular name.

Zone In a DNS database, a contiguous portion of the domain tree that is administered as a single separate entity by a DNS server. The zone contains resource records for all of the names within the zone.

Zone file A file that consists of the DNS database resource records that define the zone. DNS data that is Active Directory–integrated is not stored in zone files because the data is stored in Active Directory. However, DNS data that is not Active Directory–integrated is stored in zone files.

Zone transfer The process of copying the contents of the zone file located on a primary DNS server to a secondary DNS server. Using zone transfer provides fault tolerance by synchronizing the zone file in a primary DNS server with the zone file in a secondary DNS server. The secondary DNS server can continue performing name resolution if the primary DNS server fails.