Carrier-Grade NAT (CGNAT) lets an ISP share a smaller pool of public IPv4 addresses among many customers. The customer router receives an address that is not directly reachable from the public internet, while the ISP translates many private customer sessions to one or more public addresses.
Video walkthrough
Why ISPs use CGNAT
Public IPv4 addresses are limited. CGNAT allows providers to continue serving large numbers of customers while conserving public IPv4 space. IPv6 reduces this pressure, but real-world adoption varies by network and application.
How to recognize CGNAT
Compare the WAN IP shown on your router with the public IP reported by an external service. If they differ, NAT exists somewhere upstream. Addresses in 100.64.0.0/10 are specifically reserved for shared address space and are commonly associated with CGNAT, although other upstream NAT designs are also possible.
What usually still works
Web browsing, streaming, messaging, most app traffic, and outbound VPN connections usually work normally because the session starts from inside the network. The NAT device tracks the return traffic.
What may be difficult
Hosting a public server, exposing a CCTV recorder, accepting inbound VPN sessions, and traditional port forwarding can fail because the customer does not control the ISP's upstream NAT mapping. Some games may report a stricter NAT type, although actual gameplay quality depends more directly on latency, loss, routing, and server location.
Practical options
Ask the ISP whether a public IPv4 address is available, use IPv6 where supported, use a secure outbound tunnel to a public VPS, or use a remote-access service designed to traverse NAT. Avoid exposing management services to the internet without authentication and firewall controls.
CGNAT is not the same as congestion
CGNAT can affect inbound reachability and, if poorly scaled, can contribute to performance problems. But seeing CGNAT does not prove that it is the cause of slow browsing or high ping. Measure loss, latency, utilization, and routing before assigning blame.
Frequently asked questions
Can I port-forward through CGNAT?
Usually not from your customer router alone because another NAT layer exists upstream.
Does CGNAT always make games lag?
No. Game latency is mainly affected by routing, distance, loss, congestion, and server performance.
Can IPv6 avoid CGNAT?
With native globally routed IPv6, inbound connectivity can work without IPv4 CGNAT, subject to firewall rules and application support.
Next step
Document the result of your test and keep a known-good export. If your network behaves differently from the example, diagnose the topology rather than adding more rules blindly. Continue with a related guide from the tutorial library.