Mobile connectivity
CGNAT on Mobile Hotspots, 4G and 5G
Phone tethering and dedicated cellular routers do not expose network information in the same way. This guide explains what the addresses mean, what may be hidden, and how to investigate without guessing.
Documented development test
What an Android hotspot actually exposed
computer -> phone hotspot -> mobile carrier -> public internet
During development testing, a Windows laptop connected to an Android phone hotspot showed the observations below. This is one documented troubleshooting case, not a claim about every Android phone, mobile operator, plan, or region.
| Observation | What it established | What it did not establish |
|---|
| Laptop IPv4: 10.186.104.253 | The laptop had a private address on the phone-created local network. | It did not reveal the phone's carrier-facing WAN IPv4. |
|---|
| Default Gateway: 10.186.104.203 | The phone was the laptop's next hop for internet traffic. | The gateway value was not automatically the WAN IP required by the checker. |
|---|
| Gateway opened in a browser | No useful router status interface was exposed in this test. | The carrier-facing WAN IPv4 still could not be obtained reliably. |
|---|
Conclusion: this test documented a local phone-to-laptop NAT boundary. It did not prove that the mobile carrier used CGNAT.
Phone hotspot
The WAN comparison may be unavailable
The normal CGNATCheck method needs both the public IPv4 visible online and the WAN IPv4 shown by the router or gateway. If the phone does not expose its carrier-side address, there is no reliable value to enter. Do not substitute the phone-side Default Gateway or the computer's own local address.
CGNATCheck can still display the address visible from the internet. That tells you how the current web request appears publicly, but without the carrier-side WAN value it cannot perform the usual two-address comparison.
Dedicated cellular router
A 4G or 5G router may expose more detail
Dedicated cellular routers often have a web interface or management app closer to a conventional home router. Their connection page may expose fields such as:
- Mobile WAN IP
- Cellular IPv4
- Internet IPv4
- WAN address
Use a value only when the device labels it as an internet-facing connection address. The local admin or gateway address still serves a different purpose.
Do mobile operators always use CGNAT?
No universal statement covers every operator, plan, APN, device, region, or network mode. Mobile networks may use shared IPv4 because public IPv4 capacity is limited, but some services may expose different addressing or rely more heavily on IPv6. Treat mobile CGNAT as something to verify, not something to assume from the fact that the connection is cellular.
A WAN value in 100.64.0.0/10, when a cellular router actually exposes one, is strong shared-address evidence. A local 10.x.x.x gateway shown on a tethered computer is not equivalent evidence because it may describe only the computer-to-phone link. The IPv4 address interpretation guide explains the ranges in more detail.
What you can still determine
- Record the public-facing IP shown by the checker.
- Check whether a dedicated router exposes a real cellular WAN field.
- Confirm whether your intended app requires unsolicited inbound IPv4 traffic.
- Test whether an existing service is reachable using an external connection.
- Ask the carrier for the addressing and inbound-connectivity policy on your plan.
Questions to ask the carrier
- Does this plan receive a public IPv4 or use shared IPv4 addressing?
- Is unsolicited inbound IPv4 traffic supported?
- Is a public or static IPv4 option available for this service?
- Does the answer differ for phone tethering and dedicated mobile broadband?
- Is there an officially supported configuration for the required use case?
Android and iPhone settings vary
Android labels differ by manufacturer and software version, and iPhone menus expose only the information Apple provides for that connection. A hotspot settings page may let you change the network name, password, band, or compatibility mode without revealing the carrier WAN IPv4. The absence of that field is not itself proof of CGNAT.
Avoid changing APNs, protocol modes, or carrier settings blindly. An APN can affect how a service is provisioned, but unsupported changes can break data service or create a less secure and unreliable setup. Use carrier documentation or support guidance for your exact plan and device.
Continue with the evidence you have
If a cellular WAN IPv4 is available, enter it in the CGNAT checker. If it is not available, do not guess. Use the full WAN-IP guide for device-specific context and read what CGNAT means before asking the carrier focused questions.
