Mastering DNS: How Domain Names Turn Into IP Addresses

DNS is one of the core Internet protocols; understanding it is essential for browsing and development.

1. What is DNS?

DNS (Domain Name System) simply maps domain names to IP addresses, acting like a massive phone book. For example, the domain

math.stackexchange.com

resolves to the IP address

151.101.129.69

.

2. Query Process

Although the result is a single IP address, the DNS lookup involves several steps. The

dig

tool can display the entire process.

<code>$ dig math.stackexchange.com</code>

The command output consists of six sections:

1) Query parameters and statistics.

2) Query content (the A record request).

3) DNS server response.

4) Four A records for the domain and the TTL value (600 seconds).

5) The IP addresses of the four authoritative name servers.

6) Transmission details, including the local DNS server (e.g.,

192.168.1.253

) and response length.

Using the

+short

option simplifies the output:

<code>$ dig +short math.stackexchange.com
151.101.129.69
151.101.65.69
151.101.193.69
151.101.1.69</code>

3. DNS Servers

The local machine must know the IP address of a DNS server, which can be assigned via DHCP or configured statically in

/etc/resolv.conf

. Common public DNS servers include Google’s

8.8.8.8

and Level 3’s

4.2.2.2

. Queries can be directed to a specific server with the

@

flag:

<code>$ dig @4.2.2.2 math.stackexchange.com</code>

4. Domain Hierarchy

DNS uses a hierarchical naming scheme:

host.sld.tld.root

. The trailing dot represents the root zone, which is implicit in everyday use. The hierarchy consists of the root zone, top‑level domains (TLDs) like

.com

, second‑level domains (SLDs) such as

example

, and the host name.

<code>host.sld.tld.root</code>

5. Root Name Servers

Root servers store the NS records for the root zone. An example list includes A.ROOT‑SERVERS.NET (198.41.0.4), B.ROOT‑SERVERS.NET (192.228.79.201), and C.ROOT‑SERVERS.NET (192.33.4.12). There are thirteen root server groups in total.

6. Hierarchical Query Example

The

dig +trace

command shows the full iterative resolution process.

<code>$ dig +trace math.stackexchange.com</code>

The first section lists all root server NS records. Subsequent sections query the TLD servers, then the second‑level servers, and finally the authoritative server that returns the A records.

7. NS Record Queries

Specific NS records can be retrieved with:

<code>$ dig ns com
$ dig ns stackexchange.com</code>

Adding

+short

simplifies the output.

<code>$ dig +short ns com
$ dig +short ns stackexchange.com</code>

8. DNS Record Types

Common record types include:

A – address record (IP address).

NS – name server record.

MX – mail exchange record.

CNAME – canonical name (alias).

PTR – pointer record for reverse lookups.

Redundancy is achieved by having multiple NS, A, or MX records.

9. Other DNS Tools

host – a simplified version of

dig

that returns all records for a domain.

<code>$ host github.com</code>

nslookup – interactive query tool.

<code>$ nslookup
> facebook.github.io</code>

whois – shows domain registration information.

<code>$ whois github.com</code>

10. References

DNS: The Good Parts, by Pete Keen

DNS 101, by Mark McDonnell