RFC defines three private IP address ranges:
Class A: 10.0.0.0 to 10.255.255.255
- CIDR: 10.0.0.0/8
- Over million addresses
- Common in large enterprises
Class B: 172.16.0.0 to 172.31.255.255
- CIDR: 172.16.0.0/12
- About million addresses
- Often used in data centers
Class C: 192.168.0.0 to 192.168.255.255
- CIDR: 192.168.0.0/16
- About addresses
- Standard for home networks
Routers are configured to drop packets with these source addresses if they arrive from the internet. Your ISP will never route traffic to 192.168.x.x because that range exists on millions of separate networks.