Public IPv4
Routable on the public internet
A public IPv4 is not part of a private, shared, loopback, documentation, or other reserved block. Public does not mean a port is open; firewalls and router rules still control inbound traffic.
IPv4 reference
Public vs Private vs CGNAT IPv4 Addresses
The same-looking string of numbers can describe a device on your LAN, a router WAN connection, shared provider space, or an address visible to the public internet. Context matters as much as the range.
Private IPv4
Reused inside private networks
RFC1918 addresses are intentionally reusable and are not routed directly across the public internet. Home devices and links between two local routers commonly use them.
CGNAT shared IPv4
A provider-side shared range
The 100.64.0.0/10 block is distinct from ordinary RFC1918 space. It is intended for service-provider shared addressing and is a strong clue when shown as a router WAN IP.
Private and shared IPv4 ranges
Check the complete range. For example, not every address beginning with 100 or 172 has the same classification.
| Type | CIDR block | Visible range | Why it matters |
|---|---|---|---|
| Private IPv4 | 10.0.0.0/8 | 10.0.0.0 - 10.255.255.255 | RFC1918 private space used inside local or private networks. |
| Private IPv4 | 172.16.0.0/12 | 172.16.0.0 - 172.31.255.255 | RFC1918 private space; only the 172.16 through 172.31 portion is in this block. |
| Private IPv4 | 192.168.0.0/16 | 192.168.0.0 - 192.168.255.255 | RFC1918 private space commonly used by home routers. |
| Shared CGNAT space | 100.64.0.0/10 | 100.64.0.0 - 100.127.255.255 | Shared address space intended for service-provider networks and a strong CGNAT clue on a WAN interface. |
LAN IP, Default Gateway, and WAN IP are different fields
- Device or LAN IP
- Identifies your computer, phone, console, or server on the local network. A value such as 192.168.1.50 usually belongs only to that device inside the LAN.
- Default Gateway or Router
- Identifies the next local device that receives off-network traffic. It may help you open the router admin interface, but it is not automatically the router's WAN IP.
- WAN or Internet IPv4
- Describes the upstream side of the router or gateway. This separately labelled value is the one CGNATCheck asks you to compare.
Why a private WAN matters
If a router WAN field shows RFC1918 private space, another device or private network is upstream. In a home this is often an ISP gateway or second router. It may also be a managed building, workplace, hotspot, or provider network. The address proves an upstream private layer exists; it does not identify who operates that layer.
That is why a private WAN is handled differently from 100.64.0.0/10. Read CGNAT vs double NAT before buying a workaround or changing several router settings at once.
Practical examples
Interpret the field and the range together
PC IPv4: 192.168.1.50
Local device address
This is normally the computer's LAN identity. Do not enter it as the router WAN IP.
Default Gateway: 192.168.1.1
Route to the admin interface
This may open the router page. Look inside that page for a separate WAN or Internet IPv4 value.
Router WAN: 100.70.24.9
Shared provider-space clue
This falls inside 100.64.0.0/10 and is strong CGNAT or shared-NAT evidence.
WAN and public IP match
No strong standard-CGNAT signal
Move on to firewall, forwarding, service, and local topology checks if inbound access still fails.
Use the actual router value
First find the correctly labelled address with the WAN-IP instructions. Then run the best-effort comparison. The combination of field context, address range, and public-IP comparison is more useful than classifying a number copied from an unknown screen.