A public IP is the unique gateway address your home or office uses to communicate with the outside world. Unlike a private IP, it exists only once globally, so accurate verification is essential for remote work and server integration.
A public IP is an internet address distributed worldwide without duplication by official bodies such as ICANN and KISA (Korea Internet & Security Agency). ISPs lease these addresses to subscribers, and they are directly exposed on the internet so connection attempts are possible if the address is known. Google and Naver can return data when you browse because they know your public IP.
If a public IP is the street address for an entire building, a private IP is the room number inside — like 101 or 102. Private IPs are assigned locally by your router, so another home may use the same 192.168.0.5. Public IPs never overlap. To reach your home computer from the internet, you need the external public IP, not the private IP inside the router.
Most public IPs today use IPv4 format like 123.45.67.89, but address exhaustion is driving a gradual shift to IPv6 such as 2001:db8::ff00:42:8329. IPv6 supports 128-bit addresses so every device worldwide can receive a unique, permanent public IP.
When you run a VPN, an encrypted tunnel is built between your device and the VPN gateway. All outbound packets leave the internet using the VPN server's public IP as the source, so websites and services see the VPN provider's virtual public IP instead of your ISP's.
You need a public IP when: 1) requesting firewall (ACL) approval to allow specific users access to Synology or database services, 2) setting up Remote Desktop (RDP) to your home or office PC, 3) uploading or downloading files to a NAS from outside, or 4) mapping a domain to a specific IP for server development (DNS A record registration).