Public IP
A public IP is routable on the Internet. Websites normally see the public address used by your connection or by an intermediary such as a VPN, proxy or carrier gateway.
Private IP
Private IPv4 ranges are reserved for local networks: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. They are not routed across the public Internet.
NAT and home routers
Your router commonly translates traffic between private device addresses and one public IPv4 address. This is Network Address Translation (NAT). It lets phones, laptops and smart devices share the same Internet connection.
CGNAT
Carrier-grade NAT adds address sharing at the ISP level. Customers may receive an address from 100.64.0.0/10 on the provider side while websites see a different shared public address. This can complicate inbound connections and self-hosting.
What about IPv6?
IPv6 does not rely on the same private/public model. Unique local addresses (ULA) exist for internal use, while globally routable IPv6 addresses can be assigned directly to devices. Firewalls remain important even when NAT is not involved.