Skip to content

Split DNS — Providing Different DNS Answers for Internal and External Users

Split DNS (also called Split-Horizon DNS, Split-Brain DNS, or Split-View DNS) is a Domain Name System (DNS) architecture where the same domain name returns different DNS responses depending on where the request originates. Internal users receive private IP addresses and internal services, while external users receive public IP addresses and Internet-facing services. Split DNS improves security, performance, and network management by separating internal and external DNS views. Every Linux administrator, DevOps engineer, Cloud Architect, Platform Engineer, Site Reliability Engineer (SRE), and Network Engineer should understand Split DNS.

Learning Path

Networking Mastery → Module 6: DNS & DHCP → Lesson 6

Difficulty: Intermediate

Reading Time: 90 Minutes

Course Progress

Course: Networking Mastery

Module: DNS & DHCP

Lesson: 6 of 7

What You'll Learn

After completing this lesson, you'll be able to:

  • Understand Split DNS
  • Learn why Split DNS is needed
  • Differentiate Internal and External DNS
  • Understand Public and Private DNS Zones
  • Apply Split DNS in enterprise and cloud environments
  • Troubleshoot Split DNS issues

Prerequisites

Complete:

Why Learn Split DNS?

Imagine a company owns:

company.com

Employees access:

portal.company.com

from inside the office.

Customers access:

www.company.com

from the Internet.

Should both users receive the same IP address?

Usually:

No

Internal users often need private services, while external users should only reach public services.

What is Split DNS?

Split DNS provides:

Same Domain Name

↓

Different DNS Answers

Depending on:

  • Internal Network
  • External Internet

Example

Internal User:

portal.company.com

↓

10.10.20.15

External User:

portal.company.com

↓

203.0.113.25

Same hostname.

Different IP addresses.

Internal DNS

Internal DNS servers resolve:

  • File Servers
  • Active Directory
  • Internal Applications
  • Databases
  • Monitoring Systems
  • Kubernetes Services

Example:

db.company.com

↓

10.10.30.15

External DNS

Public DNS servers resolve:

  • Company Website
  • Public APIs
  • Email Services
  • Virtual Private Network (VPN) Gateway
  • Customer Portals

Example:

www.company.com

↓

198.51.100.25

Internal DNS Zone

Example:

company.com

↓

portal

↓

10.10.10.20

Accessible only from the internal network.

External DNS Zone

Example:

company.com

↓

www

↓

198.51.100.25

Accessible from anywhere on the Internet.

Split DNS Architecture

Internal Users

↓

Internal DNS

↓

Private Zone

↓

Private IP

Internet Users

↓

Public DNS

↓

Public Zone

↓

Public IP

Internal Resolution

Employee:

portal.company.com

Workflow:

Laptop

↓

Internal DNS

↓

Private Zone

↓

10.10.10.20

Traffic never leaves the internal network.

External Resolution

Customer:

portal.company.com

Workflow:

Browser

↓

Public DNS

↓

Public Zone

↓

198.51.100.25

The customer reaches the Internet-facing application.

Why Use Split DNS?

Benefits include:

  • Improved Security
  • Internal Resource Protection
  • Better Performance
  • Reduced Internet Traffic
  • Easier Management
  • Simplified Hybrid Cloud Access

Enterprise Example

Company Services:

Internal:

git.company.com

↓

10.10.20.50

External:

www.company.com

↓

198.51.100.20

Developers access internal Git servers while customers access only public services.

Active Directory Example

Microsoft Active Directory commonly uses internal DNS.

Example:

dc01.company.local

or

dc01.company.com

These records are typically not exposed on the public Internet.

Cloud Perspective

Cloud environments frequently implement Split DNS.

Examples:

  • Private DNS Zones
  • Public DNS Zones
  • Private Endpoints
  • Internal Load Balancers
  • Public Load Balancers

Applications inside the cloud resolve private addresses, while Internet users receive public addresses.

Hybrid Cloud Example

On-Premises

↓

Private DNS

↓

VPN

↓

Cloud

↓

Private Endpoint

External users:

Internet

↓

Public DNS

↓

Public Website

The same domain can support both environments.

Kubernetes Perspective

Kubernetes commonly uses internal DNS.

Example:

api.default.svc.cluster.local

External users access:

api.company.com

using public DNS.

Internal cluster services remain private.

Linux Perspective

Query DNS.

dig company.com

Query a specific DNS server.

dig @10.10.10.10 company.com

Query a public resolver.

dig @8.8.8.8 company.com

Display configured DNS servers.

cat /etc/resolv.conf

Split DNS Example

Internal:

mail.company.com

↓

10.10.10.50

External:

mail.company.com

↓

198.51.100.50

Users receive different answers based on where the query originates.

Advantages of Split DNS

  • Stronger Security
  • Better Performance
  • Private Resource Protection
  • Reduced Wide Area Network (WAN) Traffic
  • Flexible Network Design
  • Improved User Experience

Limitations

  • More complex DNS administration
  • Internal and external zones must remain synchronised where appropriate
  • Incorrect configuration can cause inconsistent DNS responses
  • Troubleshooting requires checking both DNS views

Hands-on Lab

Task 1

Display configured DNS servers.

cat /etc/resolv.conf

Task 2

Query a domain.

dig company.com

Task 3

Query a specific internal DNS server.

dig @10.10.10.10 company.com

Task 4

Query a public DNS server.

dig @8.8.8.8 company.com

Task 5

Compare:

  • Internal DNS
  • External DNS

Task 6

Design Split DNS for:

  • Public Website
  • Employee Portal
  • Git Server
  • VPN Gateway

Task 7

Draw the Split DNS architecture showing:

  • Internal Users
  • Internal DNS
  • External Users
  • Public DNS

Task 8

Research how Split DNS is implemented in:

  • Amazon Web Services (AWS)
  • Microsoft Azure
  • Google Cloud

Linux Commands

Command Purpose
dig domain.com Query DNS
dig @server domain.com Query a specific DNS server
nslookup domain.com Perform DNS lookup
host domain.com Display DNS information
cat /etc/resolv.conf View configured DNS servers

Common Mistakes

❌ Publishing internal IP addresses in public DNS.

✅ Keep private records only in internal DNS zones.

❌ Forgetting to update both DNS views.

✅ Synchronise shared records carefully.

❌ Using public DNS for internal services.

✅ Configure clients to use internal DNS resolvers.

❌ Assuming Split DNS replaces firewalls.

✅ Continue enforcing network security controls.

❌ Troubleshooting only one DNS view.

✅ Verify both internal and external responses.

Best Practices

  • Maintain separate internal and external DNS zones.
  • Publish only necessary public records.
  • Protect internal DNS servers from Internet access.
  • Monitor DNS consistency between zones.
  • Document internal and external DNS architectures.
  • Test name resolution from both internal and external networks.

Interview Questions

Beginner

  1. What is Split DNS?
  2. Why is Split DNS used?
  3. What is the difference between internal and external DNS?
  4. What is a private DNS zone?

Intermediate

  1. Explain how Split DNS improves security.
  2. How does Split DNS work?
  3. Compare public and private DNS zones.
  4. What are common Split DNS use cases?

Architect Level

  1. Design a Split DNS architecture for a hybrid cloud enterprise.
  2. How would you secure internal DNS infrastructure?
  3. How would you troubleshoot inconsistent DNS responses between internal and external users?

Summary

In this lesson, you learned:

  • Split DNS
  • Internal DNS
  • External DNS
  • Public DNS Zones
  • Private DNS Zones
  • Enterprise DNS Architecture
  • Hybrid Cloud DNS
  • Kubernetes DNS Integration
  • Linux DNS Query Commands

Split DNS allows organisations to return different DNS responses based on the source of the request. Internal users receive private addresses and access internal services, while external users receive public addresses for Internet-facing applications. This architecture improves security, simplifies management, and supports modern enterprise and hybrid cloud deployments.

Key Takeaways

  • Split DNS provides different DNS responses for internal and external users.
  • Internal DNS resolves private services using private IP addresses.
  • External DNS resolves public services using public IP addresses.
  • Split DNS enhances security by hiding internal infrastructure.
  • Private and public DNS zones should be managed carefully.
  • Split DNS is widely used in enterprise, cloud, and hybrid environments.

What's Next?

DNS Troubleshooting

In the next lesson, you'll learn about DNS Troubleshooting.

You'll explore:

  • Common DNS Problems
  • DNS Resolution Failures
  • DNS Cache Issues
  • DNS Propagation
  • Diagnostic Tools
  • Linux DNS Troubleshooting Commands
  • Enterprise Troubleshooting Methodology

By the end of the lesson, you'll be able to diagnose and resolve common DNS issues using systematic troubleshooting techniques and Linux networking tools.