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OOTW / Chapter I - Foundation / 04. Web Foundations / 03. Domain

Domain

When a user visits:

https://operatoronthewire.com

the computer cannot actually connect to:

operatoronthewire.com

Computers communicate using IP addresses:

104.21.96.1
172.67.182.45
192.168.1.10

DNS exists to translate human-friendly names into IP addresses.

What Is a Domain?

A domain is simply a name assigned to a resource.

Examples:

google.com
operatoronthewire.com
microsoft.com

Instead of remembering:

142.250.191.14

humans remember:

google.com

Domain Structure

Consider:

exam.operatoronthewire.com

Breaking it apart:

exam.operatoronthewire.com
│                        │
├── Subdomain            └── Top-Level Domain
│
└── operatoronthewire.com
      │
      └── Second-Level Domain

Top-Level Domains (TLDs)

Examples:

.com
.net
.org
.edu
.gov
.io
.dev

These are managed by global registries.

Second-Level Domains

Examples:

google.com
microsoft.com
operatoronthewire.com

This is usually what people purchase.

Subdomains

Examples:

www.operatoronthewire.com
blog.operatoronthewire.com
api.operatoronthewire.com
portal.operatoronthewire.com

Organizations can create as many subdomains as they want.

Internal Domains

Organizations often maintain internal DNS.

Examples:

corp.local
internal.company.com
ad.company.com

These records may not exist publicly.

Active Directory and DNS

Active Directory relies heavily on DNS.

Examples:

dc-1.corp.local

_ldap._tcp.corp.local

_kerberos._tcp.corp.local

Without functioning DNS:

Active Directory largely breaks.

Reverse DNS

Normal DNS:

Hostname
    ↓
IP

Reverse DNS:

IP
    ↓
Hostname

Example:

10.10.10.5
    ↓
dc-1.corp.local

Uses:

PTR Records

DNS Caching

Operating systems cache responses.

Example:

operatoronthewire.com
→ 104.21.96.1

Future lookups may come from cache.

Windows:

ipconfig /displaydns

Flush cache:

ipconfig /flushdns

Why Operators Care About DNS

DNS often reveals:

  • Internal hostnames
  • Mail infrastructure
  • Cloud infrastructure
  • Development environments
  • Subdomains
  • Authentication services

DNS is frequently one of the first sources of information during reconnaissance.

Examples:

vpn.company.com
mail.company.com
portal.company.com
dev.company.com
jira.company.com

Many assessments begin with DNS enumeration.

Operator Notes

When a user enters:

https://portal.operatoronthewire.com

the simplified process is:

1. DNS resolves portal.operatoronthewire.com
2. Browser obtains IP address
3. TCP connection established
4. TLS handshake occurs
5. HTTP requests begin

Most Internet communication ultimately starts with DNS.

Without DNS, users would need to remember IP addresses for every service they wish to access.