Private IP Definition

RFC 1918

10.0.0.0/255.0.0.0(8)

172.16.0.0/255.240.0.0(12)

192.168.0.0/255.255.0.0(16)

RFC 6598

100.64.0.0/255.252.0.0 (10) 

ISP internal

RFC 2544

192.18.0.0/255.127.0.0  

for a testing device were to be accidentally connected to partt of the Internet

RFC 5737

192.0.2.0/255.255.255.0 (24)

198.51.100.0/255.255.255.0 (24)

203.0.113.0/255.255.255.0 (24)

References

https://en.wikipedia.org/wiki/Private_network

https://www.ietf.org/standards/rfcs/

https://www.rfc-editor.org/search/rfc_search.php

https://tools.ietf.org/html/rfc1918

https://tools.ietf.org/html/rfc6598

https://tools.ietf.org/html/rfc2544

https://tools.ietf.org/html/rfc5737