Direct Answer
CGNAT (Carrier-Grade Network Address Translation) lets a mobile carrier share one public IPv4 address among many subscribers at once. Each device keeps a private address internally, and the carrier maps it to a unique port on the shared public IP. Because thousands of real users sit behind that one address, blocking it is impractical for most websites.
Why Carriers Ran Out of IPv4 Addresses
Demand for internet access keeps climbing, but the supply of IPv4 addresses is finite. Mobile carriers face a simple constraint: how do you connect millions of subscribers with a limited pool of IPs? The answer is a technology called Carrier-Grade NAT (CGNAT) — the same shared-IP design that gives real mobile proxies their unusually high trust profile.
What is CGNAT?
CGNAT, or Carrier-Grade Network Address Translation, lets internet service providers (ISPs) and mobile carriers assign a single public IPv4 address to many users at the same time. Each device is given a private IP address behind the scenes, and the carrier translates that private address into the shared public IPv4 address whenever the device communicates with the internet.
How Does CGNAT Work?
CGNAT maps different users' private IP addresses to different ports on a single public IPv4 address. When a device accesses the internet, its traffic is tagged with a unique port number, so the carrier can route responses back to the right device. A single IPv4 address exposes 65,535 ports per protocol, so one public IP can serve a large number of simultaneous sessions before the carrier needs another address. This lets many users share the same public IPv4 address without their connections interfering with one another. The address a mobile device gets from its carrier typically comes from the shared address space 100.64.0.0/10, which RFC 6598 reserves specifically for carrier-grade NAT.
Why is CGNAT Necessary?
The core reason is the shortage of available IPv4 addresses. The IPv4 standard uses 32-bit addressing, which caps the entire internet at roughly 4.3 billion addresses — a pool that was officially exhausted years ago. Mobile adoption has grown faster than IPv4 could keep up with. CGNAT answers this by pairing the private address space reserved in RFC 1918 on each device with a far smaller pool of shared public addresses — extending the useful life of IPv4 while the internet gradually transitions to IPv6, whose 128-bit addressing provides a vastly larger space (around 340 undecillion addresses).
What CGNAT Means for Blocking Decisions
For websites and security systems, one practical consequence stands out: it is hard to act against a single device behind a CGNAT setup, such as a device on a mobile network. Because many users share the same public IP, restricting that one address could cut off a large number of unrelated, legitimate users. The shared nature of CGNAT addresses also makes it difficult to tell whether traffic comes from one device or many. For this reason, many platforms treat mobile IPs with more caution and apply per-IP restrictions far less readily than they would for a single-user address — one of the main inputs into a mobile address's IP reputation.
Key Advantages of CGNAT
- Efficient use of IPv4 addresses: sharing one public IP across many users helps carriers manage a limited IPv4 pool.
- Uninterrupted internet access: subscribers stay online without being affected by the IPv4 shortage.
- Practical network management: carriers keep control over traffic while supporting far more users per address.
Conclusion
CGNAT is a foundational technology that helps mobile carriers meet demand despite the limits of IPv4. By letting many users share one public IP, it keeps networks running efficiently and the experience smooth for subscribers. That same shared-IP design also makes per-IP blocking a blunt instrument for websites, since restricting one address risks affecting many legitimate users. CGNAT serves as a bridge until IPv6 becomes the global standard — a temporary but essential answer to the IPv4 shortage. That shared-IP trust is also the foundation GermanProxy.io is built on: dedicated German mobile endpoints on real carrier networks.
FAQ
What does CGNAT stand for?
CGNAT stands for Carrier-Grade Network Address Translation (sometimes written LSN, large-scale NAT). It is the mechanism carriers use to let many subscribers share a single public IPv4 address, mapping each device to its own set of ports on that shared address.
Does every mobile connection use CGNAT?
Most do. Because public IPv4 addresses are scarce, mobile carriers almost always place subscribers behind CGNAT by default, handing each device a private address and translating it to a shared public IP. A dedicated public IPv4 on mobile is the exception, not the rule.
Why are CGNAT mobile IPs harder to block?
Because a single CGNAT address represents many real subscribers at once. Restricting that one IP would cut off large numbers of unrelated, legitimate users, so most platforms apply per-IP restrictions to mobile addresses far more cautiously than to single-user addresses.
Does IPv6 make CGNAT unnecessary?
In principle, yes — IPv6 has enough addresses to give every device its own, removing the need to share. In practice CGNAT remains widespread because the transition to IPv6 is gradual and much of the internet still depends on IPv4, so carriers keep using CGNAT as a bridge.
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