Chapter 1: Networking Fundamentals
1.7 Public vs private IP
A public IP is globally unique and routable on the internet. A private IP is used only inside a local network (home, college, VPC) and is not routable on the internet. RFC 1918 reserves three private ranges:
| Class | Private range (RFC 1918) | CIDR | Typical use |
|---|---|---|---|
| A | 10.0.0.0 – 10.255.255.255 | 10.0.0.0/8 |
Large companies, AWS VPCs |
| B | 172.16.0.0 – 172.31.255.255 | 172.16.0.0/12 |
AWS default VPC uses 172.31.0.0/16 |
| C | 192.168.0.0 – 192.168.255.255 | 192.168.0.0/16 |
Home Wi-Fi routers |
Other special ranges: 100.64.0.0/10 (carrier-grade NAT used by mobile ISPs) and 169.254.0.0/16 (link-local; on EC2, 169.254.169.254 is the instance metadata service).
Check your own IPs:
# Private IP(s) of this machine
ip -4 addr show
hostname -I
# Public IP as seen by the internet
curl -s https://checkip.amazonaws.com