IPv4 Private Address Ranges:
- 10.0.0.0/8 IP addresses: 10.0.0.0 — 10.255.255.255.
- 172.16.0.0/12 IP addresses: 172.16.0.0 — 172.31.255.255.
- 192.168.0.0/16 IP addresses: 192.168.0.0 – 192.168.255.255
Private IPv4 internet address ranges are defined in RFC1918 with the motivation to control growth of the internet routing tables and to preserve IPv4 addresses space to extend it’s life.
The private ranges defined in this RFC are not routable over the internet and are intended for internal use only in private Internets/Intranets and that means these packets destined to these ranges will not be routable across the internet and should stay within the private network.
IPv6 private Address Ranges:
Private IPv6 address ranges or unique local addresses (ULA) were defined in RFC4193, and they are the counterpart of the IPv4 private range that we defined above. This means that they are also not expected to be routed over the internet and are intended for local use in private networks only.
Range fd00::/8 can be used by network administrators to generate random blocks of networks for internal use.
Uses and considerations:
The most common uses for private address spaces is within private enterprise or residential networks. This allows such networks to have control their internal address space independently from their internet service provider. Private address ranges also offers a security line of defense sense these addresses are not reachable across the internet and the network administrator can easily control which devices can be reached from external networks and which can not.
It should be also noted that if the network is running BGP, these ranges should be filtered by the default configuration on border routers and should never be sent to external BGP neighbors except for L3 VPN setups.