Public vs Private IP Addresses

A public IP is the globally unique address your ISP assigns to your internet connection — it is what websites see. A private IP (like 192.168.1.5) only exists inside your local network and is invisible to the internet. You use both at the same time.

Why you have two (or more) addresses

Your router holds the public IP on its internet-facing side and hands out private IPs to every device on your network — phone, laptop, TV, printer. When a device opens a website, the router rewrites the traffic so it appears to come from the single public address; this is NAT (Network Address Translation). That is why checking your IP on two devices on the same Wi-Fi shows the same public address, while each device's own settings show a different private one.

The private (RFC 1918) ranges

Three address blocks are reserved for private networks and are never routed on the public internet. If an address falls in one of these ranges, it is private:

Range (CIDR)Addresses covered — typical use
10.0.0.0/810.0.0.0 – 10.255.255.255 — large corporate networks, some routers
172.16.0.0/12172.16.0.0 – 172.31.255.255 — business networks, Docker defaults
192.168.0.0/16192.168.0.0 – 192.168.255.255 — nearly every home router

Two related special ranges are worth knowing: 127.0.0.0/8 (loopback — 127.0.0.1 is always "this device") and 169.254.0.0/16 (link-local — a device that failed to get an address from the router).

CGNAT: when even your "public" IP is shared

Because IPv4 addresses ran out, many ISPs — especially mobile carriers — put whole groups of customers behind one shared public address using carrier-grade NAT (CGNAT). The reserved range for that middle layer is 100.64.0.0/10 (100.64.0.0 – 100.127.255.255, RFC 6598). If your router's WAN address falls in that range, you are behind CGNAT: your true public IP belongs to the carrier, hosting services from home is difficult, and websites see an address shared with other subscribers.

Router IP vs device IP vs public IP

  • Public IP — assigned by the ISP; what the internet sees. Find it on the homepage or with the IPv4 checker.
  • Router IP — the router's private address on your network, usually 192.168.1.1 or 192.168.0.1; this is where the admin page lives. See how to find your router's IP.
  • Device IP — the private address your router gave this specific device, e.g. 192.168.1.37, visible in your Wi-Fi settings.

How to tell them apart at a glance

Starts with 10., 192.168., or 172.16–172.31? Private. Starts with 100.64–100.127? CGNAT. 127.x? Loopback. Anything else is normally a public address — you can confirm with an IP lookup. For the basics behind all of this, read what an IP address is.