Always Geeky

Don’t be tempted to use any random IP address or domain for documentation or testing purposes. It is quite easy to forgot to remove such an IP or domain from a config or diagram, which can cause outages and other unintended consequences.

RFC 5737 details IPv4 address blocked which have been specifically set aside for use in documentation. These IP blocks are:
192.0.2.0/24
198.51.100.0/24
203.0.113.0/24

Of course, there is nothing stopping your from using private IP blocks for us in documentation, but you do run the risk of conflicts arising, as well as not recognizing that an IP is for documentation purposes, and not an actual IP address. The above IP blocks should be added to bogan filters, therefore hopefully preventing any production issues.

IPv6 documentation IP’s are covered in RFC 3849, being:
2001:DB8::/32

Domain names for documentation purposes are also covered, by RFC 2606. There are 3 options if you need to use a real TLD, being:
example.com
example.org
example.net.

IANA has also reserved a number of TLD specifically for documentation purposes, so any domain using a TLD of .test, .example, .invalid or .localhost is permitted.