What is CGNAT (Carrier-Grade NAT)?
A technique mobile carriers and some ISPs use to share one public IPv4 address among many subscribers at the same time.
IPv4 addresses ran out long ago, so carriers put many customers behind a single public address and translate their connections at the network edge. To a website, hundreds or thousands of phones can appear to come from the same IP.
That is what makes mobile proxies so hard to block: banning a CGNAT address would lock out a crowd of real subscribers along with the one it meant to stop. Sites know this and give such addresses more benefit of the doubt.
It cuts both ways. Being behind CGNAT on your own phone can also get you CAPTCHAs you did nothing to earn, because someone else on the same address did.
Related terms
Mobile Proxy
A proxy that routes traffic through a real 4G or 5G connection on a mobile carrier network, so the exit IP belongs to a phone operator rather than a hosting provider or a home ISP. Also called a 4G, 5G or cellular proxy.
Residential Proxy
A proxy that routes traffic through an IP address assigned by an ISP to a real home device, making requests appear to come from a genuine consumer.
CAPTCHA
A challenge designed to tell humans from bots. Clean residential IPs and good request hygiene reduce how often CAPTCHAs are triggered.
ASN (Autonomous System Number)
A unique identifier for a network operator on the internet. Targeting by ASN lets you select IPs belonging to a specific ISP or carrier.