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🔎 CGNAT Diagnosis

How to Check if Your Internet Connection Is Behind CGNAT

You set the port forwarding rule perfectly, the firewall is open, DDNS is updated — and remote access still refuses to connect. Before you change one more setting, run this two minute test.

✍️ Technical Anshu🌐 Works on Any ISP⏱️ 5 minute read
🎥 Watch the full video — the remote access method that works even behind CGNAT, shown live

CGNAT — Carrier Grade NAT — means your ISP does not give your router a real public IP at all. Your router gets a private address on the ISP's own network, and hundreds of customers share one public IP between them. In that situation port forwarding can never work, because the connection from the internet stops at the ISP's NAT — it never reaches your router. Most people waste days re-checking perfect settings. The test below settles the question in two minutes.

Router Status Page — Internet Connection
WAN IP Address shown in router100.72.44.18
Public IP shown on an IP check website49.207.131.9
Two addresses are differentCGNAT CONFIRMED
☝️ The classic CGNAT signature — the router WAN address starts with 100. and does not match your public IP
1

Find the WAN IP Inside Your Router

  1. Open your router's admin page — usually 192.168.0.1 or 192.168.1.1 — and sign in
  2. Open the Status, Internet or WAN page (the name differs by brand)
  3. Note the WAN IP address the router itself reports — this is the address your ISP actually gave your router
  4. Ignore the LAN IP range (192.168.x.x). That is your internal network and tells you nothing about CGNAT
2

Compare It With Your Public IP

  1. On any device behind that router, open a browser and search what is my IP — note the address shown
  2. Now compare the two numbers
  3. Both addresses are the same — you have a real public IP. Port forwarding can work; your problem is somewhere in the forwarding rule, the firewall, or the PC itself
  4. The addresses are different — your connection passes through another NAT layer before the internet. You are behind CGNAT
3

Read the WAN Address Range for a Faster Answer

Sometimes one glance at the WAN IP is enough.

  1. WAN IP starting with 100. and the second number between 64 and 127 (for example 100.72.x.x) — this is the reserved CGNAT range. Definite CGNAT
  2. WAN IP in 10.x.x.x, 172.16 to 172.31, or 192.168.x.x — a private address on the WAN side. Also NAT in between, often a building or society network, or a second router in your own office
  3. Any other WAN address that matches the public IP from the test — a genuine public IP
  4. One caution — if your office has two routers in a chain (the ISP device feeding your own router), the same test shows a mismatch. That is double NAT, which you can fix yourself, unlike CGNAT
4

Understand What CGNAT Breaks — and What It Does Not

  1. Broken: anything that needs the internet to connect inward to you — port forwarding, DDNS to your router, direct RDP, hosting a server people reach by your IP
  2. Working normally: browsing, downloads, video calls, cloud software — everything that connects outward
  3. This is why the failure feels so strange — the internet works perfectly, only remote access is impossible
  4. No router setting can change this. The NAT sits in the ISP's network, not in your office
5

Your Three Real Options Behind CGNAT ⭐

  1. Ask the ISP for a public or static IP — some ISPs remove CGNAT on request or sell a static IP as an add-on. As the video shows, expect an extra charge, and some ISPs refuse outright
  2. Use a mesh VPN like Tailscale — both PCs connect outward and meet in an encrypted private network, so no inbound port is needed at all. This works on every connection, CGNAT included, and is the method shown in the video
  3. Use a cloud remote access tool — works, but your office desktop then depends on a third-party service and account; read its security terms before trusting it with a server
  4. For an office server holding accounts data, option 2 is the balanced choice — private, encrypted, and under your own account's control
⚠️ Do not try to escape CGNAT by forwarding more ports or putting the PC in the router's DMZ. Behind CGNAT none of that can work, and on a connection that does have a public IP, a DMZ or open RDP port exposes the PC to the whole internet. Diagnose first, then pick a method that connects outward.

🎥 Watch the Working Method in the Full Video

The video shows the Tailscale setup that reaches an office PC from anywhere — no static IP, no port forwarding, CGNAT-proof.

▶️ Watch Full Video
❓ Frequently Asked Questions

Which Indian ISPs commonly use CGNAT?

Many local cable and fiber providers, and most mobile and fixed-wireless connections, place customers behind CGNAT by default. Some large fiber ISPs give a public IP on some plans and CGNAT on others. Do not guess by brand — run the two-address test above on your own connection; it takes two minutes and never lies.

Can DDNS fix remote access behind CGNAT?

No. DDNS only converts your changing public IP into a fixed name. Behind CGNAT that public IP belongs to the ISP and is shared with many customers, so the name points to the ISP's NAT — a door that has no forwarding rule for you and never reaches your router.

My WAN IP and public IP match, but forwarding still fails. What now?

Then CGNAT is not your problem. Check in this order — the forwarding rule points to the PC's current LAN IP (reserve it in DHCP so it never changes), Windows Firewall allows the service, and the service itself is running. Also test from outside the office network, for example from mobile data — many routers block the public address when used from inside.

This guide is based on the Technical Anshu no static IP remote access video • Stuck on any step? Ask in the video comments — help is available there 🙏