As you delve deeper into the world of domain names, DNS, and how the internet works, you'll encounter a lot of specific terminology. Understanding these terms is key to grasping the concepts discussed in various articles and for generally navigating the digital landscape.
This glossary aims to define many of the common terms we've used or that you're likely to come across. While the focus is on domains, we'll also touch upon closely related concepts in networking and internet governance.
Core Domain & Naming Components
Domain Name: A human-readable label (e.g., example.com) that identifies a location or resource on the internet. It's translated by the DNS into an IP address that computers use to connect.
Effective Top-Level Domain (eTLD) / Public Suffix: A domain under which internet users can directly register names. This includes TLDs like .com as well as public suffixes like .co.uk. The Public Suffix List (PSL) helps identify these.
Fully Qualified Domain Name (FQDN): A complete domain name that specifies its exact location in the DNS hierarchy, ending with a TLD and, implicitly, the root. Example: www.example.com. (the final dot for the root is often omitted in browsers but is part of the FQDN).
Hostname: A label assigned to a device connected to a computer network, used to identify the device. In internet terms, it's often an FQDN that resolves to an IP address (e.g., server1.example.com).
Label (Domain Label): Each part of a domain name separated by dots. For www.example.com, www, example, and com are all labels. Labels have character and length restrictions.
localhost: A special hostname that always refers to the computer currently being used (i.e., "this computer" or "itself"). It typically resolves to the IP address 127.0.0.1 (IPv4) or ::1 (IPv6).
Root Zone (DNS Root Zone): The highest level in the DNS hierarchy. It contains the delegations for all Top-Level Domains (TLDs).
Second-Level Domain (SLD): The part of a domain name registered directly under a TLD. In example.com, example is the SLD. In example.co.uk (where .co.uk is an eTLD), example is the registrable part.
Subdomain: A domain that is part of a larger domain. In blog.example.com, blog is a subdomain of example.com.
Top-Level Domain (TLD): The rightmost segment of a domain name, following the last dot (e.g., .com, .org, .uk).
Country Code Top-Level Domain (ccTLD): TLDs assigned to specific countries or territories, usually two letters long (e.g., .us, .ca, .de).
Generic Top-Level Domain (gTLD): TLDs that are not country-specific (e.g., .com, .org, .net, .info).
New Top-Level Domain (nTLD): gTLDs introduced in rounds starting around 2012 (e.g., .guru, .photo, .online).
DNS Records & Zone Files
A Record (Address Record): A DNS record type that maps a hostname to an IPv4 address.
AAAA Record (IPv6 Address Record): A DNS record type that maps a hostname to an IPv6 address.
Authoritative Nameserver: A nameserver that holds the definitive DNS records for a specific domain or zone. Queries for records within that zone are ultimately answered by an authoritative nameserver.
Class (DNS Class): Indicates the namespace of the record data. Almost always IN for Internet records.
CNAME Record (Canonical Name Record): A DNS record type that maps a hostname (an alias) to another hostname (the canonical or true name).
DNS (Domain Name System): The hierarchical and decentralized naming system used to locate computers, services, or other resources connected to the Internet or a private network. It translates domain names into IP addresses.
DNS Record: A single entry in a DNS zone file that provides information about a domain or hostname, such as its IP address, mail servers, etc.
DNSSEC (Domain Name System Security Extensions): A suite of specifications for securing certain kinds of information provided by DNS by using digital signatures to ensure data authenticity and integrity.
MX Record (Mail Exchange Record): A DNS record type that specifies the mail server(s) responsible for accepting email messages on behalf of a domain.
NS Record (Name Server Record): A DNS record type that delegates a DNS zone to use specific authoritative nameservers.
SOA Record (Start of Authority Record): A DNS record type that contains administrative information about a zone, including the primary nameserver, contact email for the domain administrator, domain serial number, and timers for refreshing the zone.
SPF Record (Sender Policy Framework): Often implemented as a TXT record, it specifies which mail servers are authorized to send email on behalf of a domain, helping to combat email spoofing.
SRV Record (Service Record): A DNS record type that specifies the hostname and port number of servers for specified services.
TTL (Time-To-Live): A value in a DNS record that specifies how long (in seconds) a DNS resolver or client should cache the record before querying for it again.
TXT Record (Text Record): A DNS record type that allows arbitrary text to be associated with a hostname, often used for SPF records, domain verification (e.g., for Google Search Console), DKIM, and other purposes.
Zone / DNS Zone: A distinct portion of the domain namespace managed by a specific organization or administrator. It contains the collection of DNS records for domains within that portion.
Zone File: A text file that contains the DNS records for a zone. It's what authoritative nameservers use to answer DNS queries.
Key Organizations & Roles
Backend Provider (Registry Backend): A company that provides the technical infrastructure and services for a TLD Registry to operate its TLD (e.g., shared registration system, nameserver infrastructure).
IANA (Internet Assigned Numbers Authority): The organization responsible for the global coordination of the DNS root, IP addressing, AS number allocation, and other Internet protocol resources. It is a function performed by PTI, an affiliate of ICANN.
ICANN (Internet Corporation for Assigned Names and Numbers): A non-profit organization responsible for coordinating the maintenance and procedures of several databases related to the namespaces and numerical spaces of the Internet, ensuring the network's stable and secure operation. It operates under a multistakeholder model.
Multistakeholder Model: A governance approach used by ICANN and other internet organizations where policy is developed through input and consensus from various groups, including governments, businesses, the technical community, academia, and civil society.
Registrant: The individual, organization, or entity that registers a specific domain name.
Registrar: An ICANN-accredited organization that manages the reservation of internet domain names. Registrants register domain names through registrars.
Registry (or Registry Operator): An organization responsible for operating and maintaining the master database of all domain names registered under a specific TLD (e.g., Verisign for .com).
RIR (Regional Internet Registry): Organizations that manage the allocation and registration of Internet number resources (IP addresses and AS numbers) within specific geographic regions of the world (e.g., ARIN for North America, RIPE NCC for Europe).
Protocols & Lookups
AXFR (Authoritative Zone Transfer): A DNS protocol mechanism for replicating entire zone files from a primary nameserver to secondary nameservers. If misconfigured, it can allow unauthorized parties to download an entire zone.
dig (Domain Information Groper): A command-line network administration utility for querying DNS nameservers.
HTTP/HTTPS (Hypertext Transfer Protocol / Secure): The foundational protocols for data communication for the World Wide Web. RDAP uses HTTPS.
IXFR (Incremental Zone Transfer): A DNS protocol mechanism for replicating only the changes made to a zone file from a primary nameserver to secondary nameservers.
JSON (JavaScript Object Notation): A lightweight data-interchange format that is easy for humans to read and write and easy for machines to parse and generate. RDAP often uses JSON for its responses.
Port 43: The standard TCP port traditionally used by the WHOIS protocol.
RDAP (Registration Data Access Protocol): A modern protocol designed to eventually replace WHOIS, providing access to domain name registration data in a standardized, machine-readable (JSON) format, typically over HTTPS.
Resolve-DnsName: A PowerShell cmdlet for performing DNS queries.
WHOIS (protocol): A query and response protocol widely used for querying databases that store the registered users or assignees of an Internet resource, such as a domain name or an IP address block.
Operational & Technical Concepts
ACL (Access Control List): A list of permissions attached to an object, specifying which users or system processes are granted access to objects, as well as what operations are allowed on given objects. Relevant for securing nameservers against unauthorized AXFR.
AS Number (Autonomous System Number): A unique number assigned to an Autonomous System (AS). An AS is a collection of IP routing prefixes under the control of one or more network operators that presents a common, clearly defined routing policy to the internet.
Caching (DNS Caching): The process by which DNS resolvers and operating systems store recent DNS lookup results locally for a period (defined by the TTL) to speed up subsequent requests for the same resource and reduce load on authoritative nameservers.
Delegation (DNS Delegation): The process of assigning responsibility for a portion of the DNS namespace (a zone) to a set of nameservers. For example, the .com TLD registry delegates authority for example.com to the nameservers specified for that domain.
EPP Status Codes (Domain Status Codes): Codes defined by the Extensible Provisioning Protocol (EPP) that indicate the status of a domain name registration (e.g., ok, clientTransferProhibited, redemptionPeriod).
IP Address (Internet Protocol Address): A numerical label assigned to each device participating in a computer network that uses the Internet Protocol for communication.
IPv4 Address: The fourth version of IP, using 32-bit addresses (e.g., 192.0.2.1).
IPv6 Address: The latest version of IP, using 128-bit addresses to provide a vastly larger address space (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334).
Parking Page (Domain Parking): A webpage displayed for a registered domain name that is not currently associated with an active website. It often indicates the domain is "parked" or "coming soon."
Port Number (Networking Port): A number used to identify a specific process or type of network service running on a host computer in an IP network. For example, web traffic (HTTP) typically uses port 80.
Primary Nameserver (Master): In a DNS zone transfer configuration, the authoritative nameserver that holds the original, editable copy of the zone file.
Propagation (DNS Propagation): The process by which updates to DNS records spread across the internet's DNS infrastructure. It can take some time for changes to be visible globally due to caching.
Redaction (of WHOIS Data): The process of obscuring or removing PII from public WHOIS records, often in response to privacy regulations like GDPR.
Reverse Proxy: A server that sits in front of web servers and forwards client (e.g., web browser) requests to those web servers. Often used for load balancing, security (WAF), caching, or SSL termination.
Secondary Nameserver (Slave): In a DNS zone transfer configuration, an authoritative nameserver that receives a copy of the zone file from a primary nameserver via AXFR or IXFR.
URI (Uniform Resource Identifier): A string of characters used to identify a name or a resource on the Internet.
URL (Uniform Resource Locator): A specific type of URI that not only identifies a resource but also specifies how to access it (the protocol, like HTTP or FTP) and its location. Commonly known as a web address.
Conclusion
The world of domains and internet infrastructure has its own language, but hopefully, this glossary helps demystify some of the common terms you'll encounter. As you continue to learn, referring back to these definitions can provide a solid foundation for understanding more complex topics.