split DNS
also: split-horizon DNS, view-based DNS
Split DNS is a configuration where different DNS results are returned to clients based on their network location—typically serving internal IP addresses to internal users and public IP addresses to external users.
Split DNS (also called split-horizon DNS) allows an organization to maintain separate DNS zones for the same domain name. Internal clients connecting from within the corporate network receive DNS responses pointing to private IP addresses, while external clients on the public internet receive responses pointing to public IP addresses.
This is commonly implemented using two DNS servers: one authoritative for internal queries (often behind a firewall) and one for external queries. For example, mail.example.com might resolve to 192.168.1.10 internally but 203.0.113.50 externally.
Split DNS provides security benefits by hiding internal infrastructure from the public internet, simplifies network management by allowing different routing for internal and external traffic, and enables seamless access to resources whether users are in the office or on VPN. Modern implementations often use DNS views in BIND or similar DNS servers to conditionally return different answers based on the client's source IP address.