Certain IP addresses and domain names have been reserved for documentation purposes to avoid conflicts with valid addresses in actual networks. These are defined in various RFCs (Request for Comments), which are documents that describe the protocols, procedures, and policies used on the Internet.
IP Subnets Reserved for Documentation
The following IP address ranges have been specifically reserved for use in documentation and are not routable on the public Internet:
- IPv4:
- 192.0.2.0/24 (TEST-NET-1) — RFC 5737
- 198.51.100.0/24 (TEST-NET-2) — RFC 5737
- 203.0.113.0/24 (TEST-NET-3) — RFC 5737
- IPv6:
- 2001:DB8::/32 — RFC 3849
These ranges are meant to be used in examples, documentation, books, and other educational or illustrative materials.
Domain Names Reserved for Documentation
RFC 2606 and RFC 6761 reserve specific domain names that are intended for use in documentation. These domain names are:
- .example — for use in examples
- .test — for use in tests
- .localhost — typically used to refer to the local computer
- .invalid — used for clearly invalid domain names
Additional Reserved Domains for Documentation (RFC 6762)
RFC 6762, which specifies the multicast DNS (mDNS), reserves the following special-use domain names:
- *.local — used for local network multicast DNS
Purpose and Benefits
Using these reserved IP addresses and domain names in documentation and educational material helps prevent conflicts and security risks associated with accidentally connecting to real services or revealing valid network addresses. They ensure that examples in the documentation do not interfere with real deployments and provide a safe sandbox for learning and experimenting.
These RFCs clearly indicate which addresses and names can be safely used for testing and documentation, ensuring that educational and testing setups do not accidentally overlap with production environments.