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Proxy glossary

What is CGNAT (carrier-grade NAT)?

CGNAT is carrier-grade NAT, where an internet provider puts many customers behind a small set of shared public IP addresses.

CGNAT explained

Also called carrier-grade NAT or CGN.

IPv4 addresses ran short, so some providers, mobile carriers especially, stopped giving each customer a public address. Customers get a private one, often from the 100.64.0.0/10 block that RFC 6598 reserved for this, and the provider translates many of them onto one public IP at its edge.

A site sees that public IP and cannot tell the customers apart. One person behind it hammering a login page, or a bot, can get the shared address rate limited or flagged for everyone. Sites therefore tend to be more forgiving of these addresses, since blocking one can lock out thousands of real users, but their limits can still trip on volume that no single user produced.

It shows up in your own setup too. If your connection is behind CGNAT you have no public IP of your own, and inbound connections to your machine will not arrive. Do not allowlist that address at a proxy: every other subscriber behind the same shared IP could then use your proxy. Use username and password authentication instead.

For IP reputation, the question to ask of any address is how many others are behind it. A dedicated IP has one owner. A CGNAT address can have hundreds, and their behaviour is your behaviour.

For example

Your bot works for an hour on a home-connection IP and then meets CAPTCHAs on every page. Nothing you sent was excessive. Other households behind the same public address were hitting the same site, and it counted them all as one client.

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