Simple definition
Split DNS, also called split-horizon DNS, lets the same domain name return different answers depending on where or how the query is made.
Technical definition
The same DNS namespace can be published through internal and external views. Internal resolvers may return private addresses, while public authoritative DNS returns public addresses or no record for names that should remain internal.
How it works / role
The mechanism relies on directing each client to the appropriate DNS view according to its network, resolver, or configured policy. Internal devices normally query corporate DNS; Internet clients use the public view. VPN clients must receive the correct resolvers and search suffixes.
What is it used for?
Keep identical application names inside and outside the organization while directing users to different resources or addresses.
Practical example
app.example.com resolves to 10.20.0.15 on the LAN but to the public reverse-proxy address when queried from the Internet.
Common issues
- The internal view or zone is missing
- DNS cache contains an outdated answer
- A VPN client uses a public resolver
- Internal and external records are inconsistent
Key takeaway: Split DNS depends on both zone content and the actual resolution path used by each client.