split horizon DNS
also: split-view DNS, split DNS
A DNS configuration technique where different DNS responses are returned to clients based on whether they're querying from inside or outside a private network, allowing the same domain to resolve to different IP addresses for internal and external users.
Split horizon DNS (also called split-view DNS) maintains two separate DNS views of the same domain name. Internal clients on a private network receive one set of DNS records, while external clients on the public internet receive different records.
This is commonly used to provide internal-only services with private IP addresses to employees, while external users see only public-facing services. For example, internal.example.com might resolve to 192.168.1.10 for office computers but not resolve at all for internet users, or it might resolve to a different public IP for external queries.
Implementation typically involves running separate DNS servers (or views within a single server like BIND) that respond based on the source IP of the query. A recursive resolver on the internal network queries the internal DNS view, while external queries hit a different authoritative or caching server.