# Key Concepts & Terminology

Understanding DNS terminology is essential for configuring, troubleshooting, and maintaining high-availability content delivery.\
This page explains how key DNS components — such as domains, zones, and records — interact in the resolution process, and how they map directly to **Medianova’s DNS and CDN Resource management system**.\
Each concept is presented with both a standard definition and its role in the Medianova platform.

### **Domain**

A **domain** is a named node within the DNS hierarchy. It provides a readable identifier for services without exposing their physical or IP-level location.\
Domains are structured from right to left:

| Level         | Example   | Description           |
| ------------- | --------- | --------------------- |
| **TLD**       | `.com`    | Top-Level Domain      |
| **SLD**       | `example` | Second-Level Domain   |
| **Subdomain** | `www`     | Host or service label |

A complete domain, when ending with a trailing dot (`.`), forms a **Fully Qualified Domain Name (FQDN)**.\
Within **Medianova**, customer CDN resources are often accessed via **custom subdomains** such as `cdn.yourdomain.com`, mapped through a CNAME record to a Medianova hostname like `yourzonename.mncdn.com`.\
See [CNAME & SSL.](https://clients.medianova.com/products/performance-cdn/static-content-delivery/advanced-configuration/cname-and-ssl)

### **Fully Qualified Domain Name (FQDN)**

An **FQDN** uniquely identifies a host or service within the DNS hierarchy.\
It consists of a subdomain (or host), second-level domain, top-level domain, and an implicit root.

Example:

```
www.example.com.
```

Medianova CDN configurations frequently reference FQDNs to associate a CNAME record with a specific **CDN Resource** or **Redirect** domain.\
→ See [Redirect](https://clients.medianova.com/products/dns/redirect) for domain-level forwarding examples.

### **Zone**

A **zone** defines the administrative boundary for a portion of the DNS namespace.\
It includes:

* **SOA (Start of Authority)** record
* **NS (Nameserver)** records
* Resource records such as A, CNAME, TXT, or MX

A zone can represent an entire domain (e.g., `example.com`) or a delegated subdomain (e.g., `media.example.com`).\
In **Medianova DNS**, each customer-configured resource (CDN or Redirect) operates within its own **zone**, managed via the [Medianova DNS Service](https://clients.medianova.com/products/dns/medianova-dns-service).

### **Record**

A **DNS record** is a data entry within a zone that maps a domain name to specific information — such as IP addresses, hostnames, or metadata.\
Each record includes:

* **Name** – Domain or subdomain the record applies to
* **Type** – Record category (e.g., A, MX, TXT)
* **TTL** – Cache duration in seconds
* **Value** – Target address or data

Example:

```
www.example.com. 3600 IN A 203.0.113.10
```

Medianova primarily uses **A**, **AAAA**, and **CNAME** records to connect user domains to CDN edge endpoints.

### **Nameserver**

A **nameserver** stores and serves DNS zone data. There are two major types:

<table><thead><tr><th width="236.99993896484375">Type</th><th>Description</th><th>Medianova Context</th></tr></thead><tbody><tr><td><strong>Authoritative nameserver</strong></td><td>Responds with verified zone records for a domain.</td><td>Medianova operates authoritative Anycast nameservers (<code>ns1.medianova.com</code>, <code>ns2.medianova.com</code>) for customer zones.</td></tr><tr><td><strong>Recursive resolver</strong></td><td>Resolves queries on behalf of clients by traversing the DNS hierarchy.</td><td>Typically external (e.g., <code>8.8.8.8</code>, <code>1.1.1.1</code>); interacts with Medianova authoritative servers during lookups.</td></tr></tbody></table>

Authoritative nameservers are the ultimate source of truth for a zone, while recursive resolvers handle caching and query acceleration.

### **Delegation**

**Delegation** transfers administrative control of a subdomain to a different set of nameservers.\
This is achieved by defining `NS` records in the parent zone that point to the authoritative nameservers of the child zone.

Example:

```
shop.example.com.  IN  NS  ns1.shopdns.net.
shop.example.com.  IN  NS  ns2.shopdns.net.
```

Medianova supports delegation for organizations managing multiple environments — such as separating `cdn.example.com` for CDN traffic from `mail.example.com` for mail services.

### **TTL (Time To Live)**

**TTL** defines how long a DNS record can be cached by resolvers and clients before a refresh is required.\
Short TTLs allow faster propagation of changes but increase query volume; longer TTLs reduce DNS load but delay updates.

In **Medianova DNS**, TTL values can be adjusted per record to balance performance and flexibility — especially useful for **Redirects** or **failover configurations** that require rapid updates.

### **Recursive Resolver vs. Authoritative Nameserver**

<table><thead><tr><th width="200">Function</th><th width="263">Recursive Resolver</th><th>Authoritative Nameserver</th></tr></thead><tbody><tr><td><strong>Role</strong></td><td>Intermediary client-side resolver</td><td>Source of truth for domain or zone</td></tr><tr><td><strong>Caching</strong></td><td>Yes (per TTL)</td><td>No</td></tr><tr><td><strong>Starts from Root?</strong></td><td>Yes</td><td>No</td></tr><tr><td><strong>Answers Final Queries?</strong></td><td>Only if cached</td><td>Yes</td></tr><tr><td><strong>Examples</strong></td><td><code>8.8.8.8</code>, <code>1.1.1.1</code></td><td><code>ns1.medianova.com</code>, <code>ns2.medianova.com</code></td></tr></tbody></table>

### Fully Qualified Domain Name (FQDN)

An FQDN is an absolute, unambiguous name that fully specifies a location in the DNS hierarchy. It includes:

* Subdomain or host (e.g., `www`)
* Second-level domain (e.g., `example`)
* TLD (e.g., `com`)
* Implicit root (`.`)

Example: `www.example.com.` is an FQDN, while `example.com` is a relative name without context.

### Zone

A zone defines a set of DNS records under a single administrative boundary. While a domain is a naming concept, a zone is a configuration unit that contains:

* An SOA (Start of Authority) record
* NS (Nameserver) records
* Resource records (A, CNAME, TXT, etc.)

A zone can span an entire domain (e.g., `example.com`) or a delegated subdomain (e.g., `internal.example.com`).

Zones are hosted on authoritative nameservers and define how DNS queries should be answered for the records they contain.

### Record

A record is a single entry within a DNS zone. Each record maps a domain name to a specific piece of information—most commonly an IP address, but also mail servers, service metadata, or cryptographic keys.

Every DNS record includes:

* **Name**: The label or subdomain it applies to
* **Type**: The kind of record (e.g., A, MX, TXT)
* **TTL**: How long the record can be cached
* **Value**: The actual data (e.g., IP address, hostname)

Example:

```
www.example.com. 3600 IN A 203.0.113.10
```

### Nameserver

A nameserver is a server that stores and serves DNS zone data. There are two main types:

* **Authoritative nameserver**: Responds with the actual DNS records for a domain or zone.
* **Recursive resolver**: Acts on behalf of clients to resolve queries, starting from the root if necessary.

Authoritative nameservers are the source of truth for a zone, while recursive resolvers are intermediaries that cache and accelerate lookups.

### Delegation

Delegation occurs when a zone administrator assigns authority over a subdomain to a different set of nameservers. This is implemented by placing `NS` records in the parent zone pointing to the nameservers of the child zone.

For example:

* `example.com` may delegate `shop.example.com` to another DNS provider or system.
* The parent zone retains the `NS` record, but the child zone becomes independently administrable.

### TTL (Time To Live)

TTL is a numeric value (in seconds) that defines how long a DNS record may be cached by resolvers and clients.

* Short TTLs allow rapid changes but increase query traffic.
* Long TTLs reduce load but may delay propagation of updates.

TTL strategy is a critical component of DNS performance and reliability tuning.

### Recursive Resolver vs Authoritative Nameserver

| Function               | Recursive Resolver                         | Authoritative Nameserver               |
| ---------------------- | ------------------------------------------ | -------------------------------------- |
| Role                   | Client-side intermediary                   | Source of truth for a domain/zone      |
| Caching                | Yes (per TTL)                              | No                                     |
| Starts from Root?      | Yes                                        | No                                     |
| Answers Final Queries? | Only if cached                             | Yes (with exact data)                  |
| Examples               | `8.8.8.8` (Google), `1.1.1.1` (Cloudflare) | `ns1.medianova.com`, `ns2.example.com` |