January 3, 2025 11 min to read

Understanding DNS - How Domain Name System Works

A comprehensive guide to DNS architecture, types of DNS servers, and record types

Overview

Let’s explore how DNS (Domain Name System) works, from basic concepts to detailed operations.

Introduction to DNS

DNS (Domain Name System) is the internet’s phonebook, translating human-friendly domain names (like www.example.com) into machine-readable IP addresses (like 192.0.2.1) that computers use to identify each other on the network. This translation is essential because humans find it easier to remember domain names than strings of numbers.

Working Process

1. User accesses website (www.a.com)
2. Computer checks local DNS cache
3. If not in cache, DNS query begins
4. Root DNS server IP address is obtained
5. Query sent to Root DNS for TLD server address
6. Query sent to TLD DNS for Authoritative DNS server address
7. Query sent to Authoritative DNS for IP address
8. IP address cached and returned to browser

What is DNS?

DNS (Domain Name System) is a system that converts human-readable domain names into IP addresses used by computers on the internet.

DNS Resolution Process in Detail

📊 DNS Working Process Flowchart

📝 DNS Record Types

Common DNS Records

A Record:     Domain name → IPv4 address
CNAME:        Domain alias → Another domain
MX:           Mail server priority
NS:           Authoritative nameserver
TXT:          Text information
SPF:          Email sender verification
SRV:          Service location
AAAA:         Domain name → IPv6 address
SOA:          Zone authority information
PTR:          IP address → Domain name (reverse DNS)

Advanced DNS Records

NSID:         Nameserver identifier
DNSKEY:       DNSSEC public key
CAA:          Certificate Authority Authorization
TLSA:         TLS certificate association
SSHFP:        SSH public key fingerprint
DNAME:        Domain redirection
NAPTR:        Naming Authority Pointer

DNS Security (DNSSEC)

Configuration Examples

TinyDNS Record Format

.    SOA, NS, A
&    NS, A
@    MX, A
=    PTR, A
+    A
'    TXT
^    PTR
C    CNAME
Z    SOA
%    Client location condition
#    Comment
-    Disable A record
:    Custom
6    AAAA, PTR
3    AAAA

BIND forwarding zone example

$TTL 1D
@       IN  SOA     ns.somaz.com. root.somaz.com. (
                        0       ; serial
                        1D      ; refresh
                        1H      ; retry
                        1W      ; expire
                        3H )    ; minimum

        IN  NS      ns.somaz.com.
        IN  A       172.17.5.10

ns      IN  A       172.17.5.10
www     IN  A       172.17.5.10

BIND reverse zone example

$TTL 1D
@       IN  SOA     ns.somaz.com. root.somaz.com. (
                        0       ; serial
                        1D      ; refresh
                        1H      ; retry
                        1W      ; expire
                        3H )    ; minimum

        IN  NS      ns.somaz.com.
        IN  A       172.17.5.10

10      IN  PTR     ns.somaz.com.
10      IN  PTR     www.somaz.com.

Practical DNS Configuration Examples

DNS Load Balancing with Multiple A Records

example.com.    IN  A   192.0.2.1
example.com.    IN  A   192.0.2.2
example.com.    IN  A   192.0.2.3

GeoDNS Configuration (PowerDNS with GeoIP)

-- PowerDNS Lua script for GeoDNS
function geoip(dq)
  local country = dq.remoteaddr:toString():geoip('country')
  
  if country == 'US' then
    return {
      {qtype=pdns.A, content='192.0.2.1', ttl=300}
    }
  elseif country == 'EU' then
    return {
      {qtype=pdns.A, content='192.0.2.2', ttl=300}
    }
  else
    return {
      {qtype=pdns.A, content='192.0.2.3', ttl=300}
    }
  end
end

AWS Route 53 Weighted Round Robin Example (JSON)

{
  "Changes": [
    {
      "Action": "CREATE",
      "ResourceRecordSet": {
        "Name": "www.example.com",
        "Type": "A",
        "SetIdentifier": "Server 1",
        "Weight": 70,
        "TTL": 300,
        "ResourceRecords": [
          {
            "Value": "192.0.2.1"
          }
        ]
      }
    },
    {
      "Action": "CREATE",
      "ResourceRecordSet": {
        "Name": "www.example.com",
        "Type": "A",
        "SetIdentifier": "Server 2",
        "Weight": 30,
        "TTL": 300,
        "ResourceRecords": [
          {
            "Value": "192.0.2.2"
          }
        ]
      }
    }
  ]
}

DNS Troubleshooting Guide

  # Check A records
  dig example.com A

  # Check MX records
  dig example.com MX

  # Trace full DNS resolution path
  dig +trace example.com

  # Query specific nameserver
  dig @8.8.8.8 example.com

  # Check DNS zone transfer (if allowed)
  dig axfr example.com @ns1.example.com

  # Check reverse DNS
  dig -x 192.0.2.1

  # View full response with timing details
  dig +stats example.com

  # Check DNSSEC validation
  dig +dnssec example.com

  # DNS lookup on Windows
  nslookup example.com

  # Flush DNS cache on Windows
  ipconfig /flushdns

  # Flush DNS cache on macOS
  sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder

  # Flush DNS cache on Linux (systemd)
  sudo systemd-resolve --flush-caches
  

DNS Best Practices

Reference

• AWS Route 53 DNS
• ICANN DNS Documentation
• RFC 1034 - Domain Names
• RFC 1035 - DNS Implementation
• RFC 4033 - DNSSEC Introduction
• DNS Security: DNSSEC - Cloudflare
• BIND 9 Documentation
• DNSStuff Tools
• DNS Best Practices - NS1