CGNAT
Also called: carrier-grade NAT, large-scale NAT
CGNAT (carrier-grade network address translation) lets an internet provider place many subscribers behind a single public IP address. It is standard practice on mobile networks, where address scarcity means thousands of customers can share one address at the same time.
IPv4 ran out of addresses. Carriers responded by assigning private addresses to subscribers and translating them onto a much smaller pool of public ones at the network edge. From the outside, all those subscribers appear as a single address.
Why it matters for proxies
CGNAT is the reason a shared mobile IP is not the liability it would be on a residential connection. On a home broadband line, an address usually maps to one household — several unrelated accounts on it is unusual. Behind CGNAT, an address legitimately carries hundreds of unrelated users, so the same observation carries almost no information.
It also means blocking a mobile address has collateral cost. Cutting off one abusive user cuts off everyone else translated onto the same address, which makes outright bans a blunt instrument on mobile ranges.
The practical consequence
Do not treat a shared mobile IP as a failure of isolation. Sharing is the native state of the network. What still has to be separate is everything else — the device identity, the storage, and the timing of what each account does.