Use these when writing documentation, or giving examples.
When you are writing documentation, or are giving someone examples, you should replace real, existing things with the information below instead.
According to RFC 6761, the following domain names can be used for these purposes:
IP-ranges (IPv4 & IPv6)
In addition to the domain names and IP-ranges, there are also some reserved top-level domains for these purposes, according to RFC 2606: