What Is CGNAT (Carrier-Grade NAT) and Why It Affects You
CGNAT (Carrier‑Grade NAT) is a large‑scale version of network address translation used by ISPs to put many customers behind a small set of public IPv4 addresses. It helps stretch limited IPv4 space, but it also breaks inbound connections, complicates gaming and P2P, and makes traditional port forwarding impossible. This guide explains how CGNAT works, how to detect it in minutes, and practical workarounds — including requesting a public IP, using a VPN with port forwarding, or adopting IPv6.
How CGNAT works (and how it differs from home NAT)
- Home NAT: your router translates many private LAN devices to one public IP.
- CGNAT: your ISP translates many customers to one (or a small pool of) public IPs at the carrier network.
Under CGNAT, your router’s WAN may have a private address (not publicly routable). Your traffic is then translated again by the ISP to a shared public IP. This “double NAT” prevents unsolicited inbound traffic from reaching your home network.
Why ISPs use CGNAT
- IPv4 exhaustion: not enough public IPv4 addresses for every customer.
- Operational simplicity: fewer public IPs to manage; easier abuse handling.
- Cost control: buying public IPv4 space is expensive; CGNAT reduces demand.
How CGNAT affects you
- No port forwarding: you cannot expose a server, CCTV, or self‑hosted service from home in the usual way.
- Peer‑to‑peer limitations: some games, P2P apps, VoIP struggle with symmetric NAT and multiple translation layers.
- Remote access headaches: inbound VPNs and admin panels won’t be reachable from the public internet.
- Reputation side effects: you share a public IP with others; if one user misbehaves, sites may rate‑limit or block the shared IP.
How to detect CGNAT (2 minutes)
- Open What is My IP and note your public IP.
- Open your router’s WAN/Internet status and check the WAN IP.
- If your router’s WAN IP is in a private range — e.g.,
100.64.0.0/10(CGNAT space),10.0.0.0/8,172.16.0.0/12, or192.168.0.0/16— you are behind CGNAT. The WAN IP will differ from the public IP shown on MyIPScan. - Optional: run DNS Lookup and WebRTC Leak Test to confirm the visible egress IPs.
CGNAT and NAT “types” (gaming)
Multiple translation layers often result in Strict/Symmetric NAT, which limits peer discovery and direct connections. Even enabling UPnP or port forwarding on your home router won’t help — the ISP’s CGNAT layer still blocks inbound traffic.
Workarounds and fixes
| Option | What it does | Pros | Cons |
|---|---|---|---|
| Request public/static IP from ISP | Moves you out of CGNAT to a unique public IP | Best long‑term fix; enables port forwarding | May cost extra; not available everywhere |
| Use a VPN with port forwarding | Tunnels outbound to a server that gives you an open port | Works even under CGNAT; quick to deploy | Added latency; depends on provider support |
| Reverse tunnel / remote access relay | Initiate an outbound tunnel from home (e.g., to a VPS) and access services via that endpoint | Fine‑grained control; can secure with auth/MFA | More setup; requires hosting endpoint |
| Adopt IPv6 for inbound | Use globally routable IPv6 with firewall rules | No NAT; direct end‑to‑end connectivity | Apps/sites must support IPv6; configure firewalls carefully |
Security notes
- CGNAT is not a security product; it only translates addresses. Keep firewalls and OS security enabled.
- If you expose services (via VPN port‑forward or IPv6), use strong auth, TLS, and limit IP ranges where possible.
- Monitor logs on routers and servers; rotate credentials and keys periodically.
Checklist: diagnose & fix
- Confirm CGNAT: compare router WAN IP vs public IP on What is My IP; look for
100.64.0.0/10or other private ranges on WAN. - Decide your goal: gaming NAT type, hosting a service, or remote access.
- Pick a path: request public/static IP from ISP, or use a VPN with port forwarding, or set up a reverse tunnel, or use IPv6.
- Test: validate reachability and leaks with WebRTC and DNS.
Test now: See your public IP on What is My IP, then verify DNS and browser exposure using DNS Lookup and WebRTC Leak Test.