What is CGNAT? Why ISPs Share IP Addresses

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Summary
Learn what Carrier-Grade NAT (CGNAT) is, why ISPs in Bangladesh use it heavily, and how to check if your connection is behind CGNAT.

What is CGNAT? Why ISPs Share IP Addresses

Direct Answer: CGNAT (Carrier-Grade NAT) is a technology used by Internet Service Providers (ISPs) to share a single Public IP address among hundreds of different customers. Instead of giving your home router its own unique public address, the ISP puts your router behind a massive, ISP-level router, creating a “Double NAT” situation.

Why ISPs in Bangladesh Use CGNAT Heavily

The internet relies on IPv4 addresses, and the global supply ran out years ago. Because ISPs in Bangladesh are growing rapidly, they cannot acquire enough unique Public IP addresses to give one to every new subscriber.

To solve this, they implemented CGNAT. Just as your home router uses NAT to share one IP among your 5 phones and laptops, the ISP uses CGNAT to share one Public IP among 500 different households.

This saves the ISP immense amounts of money and allows them to continue adding subscribers despite the IPv4 shortage.

The Problems with CGNAT

For 90% of users, CGNAT is completely invisible. Browsing, streaming Netflix, and scrolling Facebook work perfectly. However, if you are a power user, CGNAT causes significant problems because you do not have a direct route to the internet.

  1. “Strict NAT” in Gaming: Because your traffic goes through your router’s NAT, and then the ISP’s CGNAT (“Double NAT”), gaming consoles struggle to establish peer-to-peer connections. This leads to dropped lobbies and voice chat failures.
  2. No Port Forwarding: If you want to access your home CCTV cameras or a home server from outside, you need to forward ports. You cannot do this on CGNAT because you do not control the ISP’s massive router.
  3. IP Bans: If another user sharing your ISP’s CGNAT Public IP engages in malicious behavior (like spamming or hacking) and gets IP-banned by a website, you will be blocked from that website too, even though you did nothing wrong.

How to Check if You Are Behind CGNAT

  1. Log into your home router’s administrative dashboard (usually 192.168.0.1 or 192.168.1.1).
  2. Look for the WAN IP or Internet IP on the status page.
  3. If that IP address begins with 10., 172.16. to 172.31., 192.168., or specifically 100.64. to 100.127. (the official CGNAT block), you are behind CGNAT.
  4. Verify this by going to whatismyip.com. If the IP address shown on the website is different from the WAN IP in your router, you are definitely behind CGNAT.

How to Bypass CGNAT

There is only one permanent way to bypass CGNAT in Bangladesh: Buy a Real IP.

By paying your ISP an additional monthly fee (usually 150-300 BDT), they will remove your connection from the CGNAT pool and assign a Dedicated Public IP directly to your router, restoring your ability to port forward and achieve an “Open NAT” for gaming.

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