What is DNS? Name Resolution for Networks

The Problem DNS Solves

IP addresses are hard to remember. 93.184.216.34 is example.com — but no one types that. Domain Name System (DNS) is the internet's address book: you ask for a name, and DNS returns the IP address your computer actually needs to make the connection.

Without DNS, every browser bookmark, email client setting, and internal tool reference would need to store an IP address directly. Any time a server moved or an IP changed, everything pointing to it would break. DNS lets names stay stable while the underlying IPs change independently.

How DNS is Structured

DNS is a global, hierarchical system:

. (root — implied, but always present)
└── com  (TLD — Top Level Domain)
    └── example.com  (registered domain)
        ├── www.example.com   (hostname)
        └── mail.example.com  (hostname)

Each level of the hierarchy is managed by a different authority. The root is managed by IANA, TLDs like .com and .uk by their respective registries, and individual domains by whoever registered them (you, in the case of your own domain).

Common DNS Record Types

For day-to-day network management, A records and PTR records are the ones you will create most often — one to resolve a hostname to an IP, and one to reverse-resolve an IP back to a hostname.

How Resolution Works

When you type www.example.com in a browser, your device follows this chain:

1. Local cache and hosts file — the device checks whether it already has a recent answer stored. The hosts file (C:\Windows\System32\drivers\etc\hosts on Windows) is checked before DNS.
2. Recursive resolver — if not cached, the device asks its configured DNS server (usually your router or your ISP). The resolver does the heavy lifting.
3. Root servers — the resolver asks a root server: "Who knows about .com?" The root refers it to the .com TLD nameservers.
4. TLD nameservers — the .com servers say: "For example.com, ask these nameservers."
5. Authoritative nameserver — the resolver asks example.com's own DNS server: "What is the IP for www?" It returns the A record.
6. Cached and returned — the resolver caches the answer for the record's TTL (e.g., 1 hour) and returns it to your device.

This whole chain typically completes in 20–100 milliseconds on a first lookup and is near-instant for cached records.

Internal DNS for Your Network

Public DNS only knows about public domain names. For internal resources — fileserver, printer.office, intranet.corp — you need internal DNS.

An internal DNS server:

• Resolves internal hostnames to private IP addresses
• Forwards unknown queries to an upstream public resolver
• Can give different answers inside vs outside the network (split DNS — see below)
• Can block DNS-based ad and malware domains if you run something like Pi-hole

For a small business, a DNS server built into your router, a Pi-hole, Windows DNS, or dnsmasq on a small Linux box is usually sufficient.

Split DNS

Split DNS (or split-horizon DNS) means your internal DNS server returns a different answer than public DNS for the same name.

The most common use case: your public website example.com points to a public IP in external DNS. Inside your office, you want example.com to resolve to an internal IP — so employees hit the server directly over the LAN rather than going out through the firewall and back in again. Your internal DNS server has a zone for example.com with the internal IP; everything else is forwarded to a public resolver.

DNS and IP Management

DNS and IP address management go hand in hand. When you allocate an IP to a server, you should create:

• An A record — mapping the hostname to the new IP
• A PTR record — mapping the IP back to the hostname (used by monitoring tools, mail servers, and security scanners)

Keeping DNS and your IP records in sync prevents "mystery IPs" on the network — devices whose purpose no one can recall because there is no hostname, no DNS record, and no documentation anywhere about what they are.