CGNAT and mobile IPs: why your phone shares a public address
Carrier grade NAT, shared IPv4, and how WiFi vs LTE changes what sites see.
On a phone, “what is my IP address” often shows a number shared with thousands of other subscribers. That is CGNAT: carrier grade NAT. The mobile operator puts your device behind a huge translator so they can run millions of customers on a small pool of public IPv4 addresses. Your home fiber line might have a dedicated public IPv4. Your LTE or 5G line often does not.
What CGNAT changes
Inbound connections to “your” public IP will not reach your phone. Hosting a game from cellular usually fails. IP allow lists at work may block you because the shared address is also used by strangers. Abuse reports to that IPv4 can affect a whole region of the carrier.
IP geolocation for CGNAT pools is coarse: a city or a whole country. An IP tracker that pins a house to a mobile IP is guessing.
IPv6 on the same phone may be unique even when IPv4 is shared. Always look up both.
Home IP versus mobile IP
Home: one router, often one public IPv4 for the LAN, maybe IPv6 for each device. Mobile: radio network, CGNAT, IP that jumps when you change towers or toggle airplane mode.
If a login alert says “new IP, same country,” it may be you switching from WiFi to cellular. If it says a datacenter ASN, it may be a VPN.
Why this matters for hide my IP
A VPN on cellular still works: you replace the carrier’s shared IP with the VPN’s IP. Test it. Some carriers break VPNs until you switch protocol (WireGuard vs OpenVPN on 443).
Do not assume airplane mode “resets identity.” You may land in the same CGNAT pool. Cookies still know the account.
Checks that help
- Compare public IP on WiFi vs LTE on this site.
- Note whether IPv6 appears only on one of them.
- For cameras at home, do not rely on a mobile IP; use a VPN into the house.
- For IP lookup of a mobile address, trust ISP name more than the street map.
CGNAT is why two strangers can show the same public IPv4. Know which network you are on before you panic about a shared number, or before you expect a unique IP that the carrier never gave you.