RFC 1918 specifies several IP address ranges reserved for private use:

However, RFC 5737 specifies these IP address ranges for use as examples in documentation:

IPv6 has the site local (fec0::/10) and link local (fe80::/10) addresses, but these are not always adequate for documentation. RFC 3894 reserves the 2001:DB8::/32 IPv6 range for documentation.

RFC 2606 reserves these top-level domain names for documentation and testing:

Furthermore, it reserves these second-level domain names:

By tradition, particularly in regard to encryption and security, documentation uses the following personal names:

Various other names have been widely used. Some names simply serve as additional communicators (e.g., Carol, Dan), but others take on particular roles. Mallory is a malicious attacker, Trudy an intruder, and Trent acts as a neural or trusted third party.