Glossary
This glossary defines key DNS terms used in RFC 1034.
A
Alias
A domain name that is an alternative name for another canonical or primary name. Aliases are implemented through CNAME resource records.
Authoritative
A name server is authoritative for a domain or zone for which it has complete zone data. Authoritative responses are marked with the AA (Authoritative Answer) flag.
C
Cache
Local storage where resolvers or name servers store previous query results. Cached data has TTL limits and must be discarded after expiration.
CNAME (Canonical Name)
A resource record type used to map an alias to a canonical name.
Class
An RR field that identifies a protocol family or protocol instance. The most common class is IN (Internet).
Cut
A boundary point in the domain name space that marks where one zone ends and another zone begins.
D
Delegation
The process of transferring authoritative control of a portion of the domain name space from a parent zone to a child zone.
Domain
A node in the domain name space tree and all nodes below it.
Domain Name
A sequence of labels on the path from a node to the root, separated by dots.
F
FQDN (Fully Qualified Domain Name)
A complete domain name ending with the root label (dot), for example www.example.com.
G
Glue Records
Address records in a parent zone that provide addresses for name servers of a child zone, used to break circular dependencies.
I
Iterative Query
A query where the name server returns the best answer it has or a referral to other name servers, and the client is responsible for following the referrals.
L
Label
A single component of a domain name, 0-63 octets in length.
N
Name Server
A server program that stores information about part of the domain name space and responds to queries.
NS Record (Name Server Record)
A resource record that specifies the authoritative name servers for a domain.
Q
QCLASS (Query Class)
The class specified in a DNS query, typically IN (Internet).
QNAME (Query Name)
The domain name to be looked up in a DNS query.
QTYPE (Query Type)
The resource record type requested in a DNS query.
R
Recursive Query
A query where the name server fully resolves the query on behalf of the client, returning a final answer or error, never returning referrals.
Resolver
A program that issues queries to name servers on behalf of client programs.
Resource Record (RR)
The basic data unit in the DNS database, containing owner, type, class, TTL, and RDATA.
Root
The top of the domain name space tree, represented by a null label, shown as a trailing dot in domain names.
S
SOA (Start of Authority)
A resource record type containing administrative information about a zone, including serial number, refresh interval, etc.
Stub Resolver
A minimal resolver implementation that forwards all queries to a recursive name server.
Subdomain
A domain that is contained within another domain.
T
TTL (Time To Live)
The length of time, in seconds, that a resource record can be cached.
W
Wildcard
A resource record whose owner name begins with a * label, used to match names that are not explicitly defined.
Z
Zone
A contiguous portion of the domain name space managed by a single authority. A zone is defined by a zone file containing SOA and NS records.
Zone Transfer
The process of copying zone data from a primary name server to a secondary name server, using AXFR or IXFR.
Common Abbreviations
| Abbreviation | Full Name | Description |
|---|---|---|
| A | Address | Address record |
| AA | Authoritative Answer | Authoritative answer flag |
| CNAME | Canonical Name | Canonical name record |
| DNS | Domain Name System | Domain Name System |
| FQDN | Fully Qualified Domain Name | Fully qualified domain name |
| IN | Internet | Internet class |
| MX | Mail Exchange | Mail exchange record |
| NS | Name Server | Name server record |
| PTR | Pointer | Pointer record |
| RA | Recursion Available | Recursion available flag |
| RD | Recursion Desired | Recursion desired flag |
| RR | Resource Record | Resource record |
| SOA | Start of Authority | Start of authority record |
| TLD | Top Level Domain | Top level domain |
| TTL | Time To Live | Time to live |
Key Concept Comparisons
Domain vs Zone
| Concept | Definition | Scope |
|---|---|---|
| Domain | A node in the tree and all its subnodes | Logical concept |
| Zone | A contiguous portion of name space managed by a single authority | Administrative concept |
Example: The example.com domain may be divided into multiple zones (example.com, sub1.example.com, sub2.example.com)
Recursive vs Iterative
| Feature | Recursive Query | Iterative Query |
|---|---|---|
| Server Work | Full resolution | Returns referrals |
| Client Work | Minimal | Follows referrals |
| Network Traffic | Server-side | Client-side |
| Implementation Requirement | Optional | Required |
Authoritative vs Cached
| Data Type | Source | Reliability | AA Flag |
|---|---|---|---|
| Authoritative | Zone file | Highest | 1 |
| Cached | Previous query | Depends on TTL | 0 |
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