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What Is CGNAT (Carrier-Grade NAT)?

CGNAT (carrier-grade NAT) is address translation run by an internet provider instead of by your home router. It puts many subscribers behind a small pool of shared public IPv4 addresses, so one public IP carries traffic from many people at once.

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how it works

How CGNAT works

Ordinary NAT happens in your router: every device at home gets a private address such as 192.168.1.20, and the router rewrites outgoing packets to the one public IP the provider assigned. CGNAT adds a second layer inside the provider's network. Your router receives an address from the shared range 100.64.0.0/10, reserved for this purpose in RFC 6598, and a large NAT device at the carrier translates it to a public IPv4 address shared with other subscribers.

The NAT keeps subscribers apart by port. Each one's connections get their own range of source ports on the shared public IP, and the carrier logs which subscriber held which ports at which time. Carriers adopted CGNAT because IPv4 addresses ran out. Mobile networks use it almost everywhere, and many home broadband providers now use it too.

You can tell you are behind CGNAT from three signs:

CGNAT: key points
  • Your router's WAN address is between 100.64.0.0 and 100.127.255.255.
  • The WAN address differs from the public address shown by what is my IP.
  • Inbound connections such as port forwarding fail even though the router is set up correctly.
why it matters

Why CGNAT matters for proxy users

A website sees only the shared public IP, not the subscriber behind it. When a carrier IP sends a burst of traffic, the site cannot tell whether that is one heavy user or hundreds of ordinary phones. Blocking the IP would lock out real customers, so sites are cautious with carrier IPs and give them more trust than hosting ranges. That is the main reason a mobile proxy is treated differently from a datacenter proxy.

The sharing has a cost too. The IP's reputation is collective, so a carrier IP can already carry CAPTCHAs earned by someone else, and the public address can change when the carrier rebalances its NAT pool. For long account sessions a dedicated static IP is more predictable; for broad public data collection, the trust of carrier IPs is the point.

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Related terms

Terms that come up alongside CGNAT.

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CGNAT FAQs

Straight answers about CGNAT.

CGNAT uses the shared address space 100.64.0.0/10, which runs from 100.64.0.0 to 100.127.255.255. RFC 6598 reserved it for the link between a carrier's NAT and its customers.

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