ISP guide
AT&T Fiber and CGNAT: how to verify your connection carefully
AT&T Fiber customers often have different equipment, pass-through settings, and account-level configurations. If remote access or port forwarding is failing, confirm the WAN details first and then verify with AT&T support if needed.
What to keep in mind
- Pass-through or IP passthrough settings can affect how your own router sees the internet connection.
- A mismatch between the router WAN IP and detected public IP can have causes other than CGNAT.
- Regional policies and equipment combinations may matter.
Verification steps
- 1.Find the WAN IP shown by the AT&T gateway or the router behind it.
- 2.Compare that value with the detected public IP from a browser-based service.
- 3.Review gateway passthrough settings before concluding the ISP is sharing a public IPv4 address.
If you are unsure which router value to compare, use the WAN-IP guide before you run the best-effort comparison.
Connection-specific check
Identify where the address changes
AT&T gateway IP passthrough changes which downstream device receives connection details. Record the gateway status and your own router WAN value before and after any supported passthrough change so you can identify where a mismatch begins.
Ask support directly
Questions to ask your ISP
- Does my AT&T Fiber account use a shared IPv4 setup or standard public IPv4 addressing?
- Are there gateway settings or service features that would affect inbound IPv4 connectivity?
- Is there a supported configuration for customers who need direct inbound access?
FAQ
AT&T Fiber and CGNAT questions
If I use IP passthrough, does that rule out CGNAT?
Not by itself. Passthrough changes how devices inside your home are arranged, but you should still compare the WAN IP against the public IP and verify account details if you are unsure.
Is a mismatch always an ISP issue?
No. A mismatch can also come from the gateway, another router in the chain, or a misread WAN status page.