Short answer: A private IPv4 address is intended for local networks. The block 100.64.0.0/10 is shared address space reserved for service-provider use, including carrier-grade NAT (CGNAT). An address outside those ranges may be globally reachable address space, but the address alone does not prove that inbound connections work or reveal who is using it.

Recognize the common ranges

These are not interchangeable categories. RFC 6598 defines shared address space separately from RFC 1918 private-use space. The current IANA IPv4 Special-Purpose Address Registry lists both, and notes that a registry entry alone does not guarantee routability in every context.

What CGNAT means

With carrier-grade NAT, an internet provider translates traffic for multiple customers through shared public IPv4 address space. Your router can have one address on its provider-facing (WAN) side while an external IP check sees another address used farther upstream. The 100.64.0.0/10 block was reserved for this shared-address use; seeing an address in it on a provider-facing interface is a clue about the network path, not conclusive proof of the provider's exact setup.

CGNAT can affect unsolicited inbound connections, port forwarding, or hosting services because the customer may not control the upstream translation. The exact behavior depends on the provider and service. It does not mean ordinary outbound browsing is impossible, and it does not identify a particular person or household.

Check your own connection carefully

1. On a device and network you administer, note the IPv4 address shown for the router's internet/WAN connection. Use the router's documentation if the interface labels differ. Do not share screenshots that expose account details.
2. From that same network, check the public IPv4 address observed by an external service, such as this site's IP check. First disconnect any VPN or proxy you intentionally use, if safe and appropriate, because it can change the address the service observes.
3. Compare the two values. A WAN address in 100.64.0.0/10 is consistent with shared provider addressing. A private-use WAN address, or a WAN address that differs from the external result, can also arise from another router, a managed network, mobile access, or other upstream translation.
4. For a definitive answer about your account, ask your ISP whether the line uses CGNAT and whether a customer-controlled public IPv4 option is available. Do not infer a particular plan or provider policy from the address alone.

What an address check cannot establish

• A private or shared address category does not identify a subscriber, device owner, or precise location. Many unrelated networks can use the same private addresses.
• A public address observed by a website does not prove that your router accepts unsolicited inbound traffic; firewalls and translation may still block it.
• A mismatch is not by itself proof of CGNAT. A VPN, proxy, second router, workplace/school gateway, or mobile carrier can change the comparison.
• IPv4 classification says nothing by itself about your separate IPv6 path. See the IPv6 validator for address syntax only; it does not test routing or VPN coverage.

For address registration rather than address type, see the public IP registry lookup guide. For location estimates, see why IP geolocation can be imprecise. To compare a network's ordinary visibility with VPN use, open the VPN visibility matrix.

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