What Is CGNAT and How It Affects Your IP Address

Why Your Neighbor Might Share Your IP Address

Run an IP lookup from your home internet connection and you might expect to see a unique address assigned only to you. For millions of broadband and mobile users, that is no longer the case. Your ISP may be routing your traffic through Carrier-Grade NAT (CGNAT), a system that places hundreds or even thousands of customers behind a single public IP address.

CGNAT was designed to solve a practical problem. The pool of available IPv4 addresses ran dry years ago, yet the internet still runs predominantly on IPv4. Rather than migrating every customer to IPv6, many ISPs opted to share existing IPv4 addresses across multiple households. The result is that your public IP address is no longer yours alone.

This article explains how CGNAT works, what it means for your privacy, and how to check whether your connection is affected.

What CGNAT Is and Why ISPs Use It

Network Address Translation (NAT) is the process of mapping private IP addresses inside a local network to a single public IP address on the internet. Your home router performs NAT every time a device on your Wi-Fi network requests a website. The router translates the private address (such as 192.168.1.105) into the public address assigned by your ISP, then tracks which device should receive the response.

Carrier-Grade NAT (CGNAT) pushes this translation one layer deeper into the ISP’s infrastructure. Instead of giving each customer a unique public IPv4 address, the ISP assigns a private IP address to your router and performs NAT again at their data center. Multiple customers share the same public IP address when they browse the web.

ISPs adopted CGNAT for a straightforward reason. Regional Internet Registries (RIRs) such as ARIN, RIPE NCC, and APNIC exhausted their free IPv4 allocations between 2011 and 2019. Obtaining additional IPv4 blocks on the transfer market now costs between $15 and $30 per address. For an ISP with millions of customers, buying unique IPv4 addresses for everyone is economically impractical.

CGNAT allows ISPs to squeeze more users out of their existing IPv4 holdings while gradually rolling out IPv6 in parallel. Most large mobile carriers and an increasing number of fixed-line broadband providers now use CGNAT as standard practice.

How CGNAT Changes What Your IP Address Reveals

An IP address is supposed to identify a single point of connection to the internet. When multiple households share one public IP, that assumption breaks down in several ways.

IP geolocation becomes unreliable. IP lookup databases map addresses to physical locations based on ISP registration data. With CGNAT, the same public IP might be registered to a city-wide pool, meaning websites and services may place you in the wrong neighborhood or even the wrong city. If you have ever visited a local news site and seen weather for a district ten miles away, CGNAT could be the cause.

Reputation-based blocking hits innocent users. Many websites maintain IP reputation scores that block or throttle traffic from addresses associated with abuse. Because CGNAT pools are shared, one customer sending spam or scraping data can get the entire pool blacklisted. The next day, you might find yourself blocked from a forum, denied access to a financial service, or asked to complete extra CAPTCHAs because someone else on your ISP triggered a reputation penalty.

Port forwarding becomes impossible. Standard NAT allows you to configure port forwarding rules on your home router so that incoming connections reach a specific device. With CGNAT, your router does not hold a public IP address. The ISP performs the second layer of NAT, and you have no control over their equipment. This breaks peer-to-peer applications, game servers, self-hosted services, and some VPN configurations.

Law enforcement requests become imprecise. When authorities trace malicious activity back to an IP address, ISPs normally log which customer held that address at a specific time. Under CGNAT, the ISP must also track which customer was mapped to which port within the shared address pool. If logging is incomplete or retention periods are short, investigations become harder and more users come under suspicion.

CGNAT vs Traditional NAT

Traditional NAT happens inside your home. Your router receives one public IP from your ISP and assigns private IPs to every phone, laptop, and smart TV on your network. You control the router, you can configure port forwarding, and your public IP is unique to your household.

CGNAT adds a second NAT layer at the ISP level. Your router still assigns private IPs locally, but it receives a private IP from the ISP rather than a public one. The ISP then maps your traffic to a shared public IP along with traffic from dozens or hundreds of other customers.

Feature	Traditional NAT	CGNAT
Public IP per customer	Yes	No (shared)
Port forwarding	Configurable on router	Blocked
IP geolocation accuracy	High	Low to moderate
Peer-to-peer connectivity	Works with router config	Often broken
IPv4 address conservation	One per household	One per hundreds of households

The core difference is control. Traditional NAT leaves the edge of the network in your hands. CGNAT moves the edge deep inside the ISP’s infrastructure, where you have no visibility and no configuration options.

The Privacy and Security Tradeoffs

CGNAT is neither purely good nor purely bad for privacy. It creates a mixed set of effects.

On one side, sharing a public IP address adds a layer of obfuscation. When a website logs your IP, it cannot distinguish you from the other households behind the same address. Correlating your browsing activity across sessions becomes harder because your mapping to the shared IP may change. In this sense, CGNAT acts as a crude, involuntary anonymity mechanism.

On the other side, CGNAT breaks end-to-end connectivity principles that underpin internet security. Many encryption and authentication protocols assume both parties can initiate connections to each other. When CGNAT blocks incoming connections, protocols that rely on direct handshakes may fall back to relay servers or less secure alternatives.

The shared-address pool also creates a liability problem. If another customer behind your CGNAT pool engages in abusive behavior, the entire pool suffers reputation damage. You may find your IP listed on blacklist check services through no fault of your own. Resolving this requires contacting your ISP, who may not be able to isolate the offending customer quickly.

For users who run home servers, participate in peer-to-peer networks, or use certain remote access tools, CGNAT introduces concrete operational problems that no amount of router configuration can fix.

How to Tell If You Are Behind CGNAT

The simplest way to detect CGNAT is to compare the WAN IP address shown on your router with the public IP address reported by an external lookup service.

1. Log into your router’s admin panel (usually at 192.168.1.1 or 192.168.0.1).
2. Find the WAN IP address on the status or internet page.
3. Open a web browser and visit an external IP lookup tool such as ippriv.com.
4. Compare the two addresses.

If your router’s WAN IP falls within a private address range, you are behind CGNAT. The private ranges are:

• 10.0.0.0 to 10.255.255.255
• 172.16.0.0 to 172.31.255.255
• 100.64.0.0 to 100.127.255.255 (the CGNAT-specific range defined in RFC 6598)

If the WAN IP matches the public IP shown by the lookup tool, your connection uses traditional NAT and you have a dedicated public IPv4 address.

A second clue is the inability to forward ports. If you configure port forwarding on your router but external port scanners report the port as closed or filtered, CGNAT is the likely culprit.

What You Can Do About It

If CGNAT is interfering with your internet usage, several options exist.

Request a public IP from your ISP. Some providers offer a static or dynamic public IPv4 address for a monthly fee. Business plans almost always include one. Contact your ISP and ask whether they can assign a public IP to your account. The fee typically ranges from free to $10 per month.

Switch to IPv6. CGNAT only affects IPv4 traffic. If your ISP supports IPv6 and the service you are accessing also supports it, your IPv6 address is unique and globally routable. Enabling IPv6 on your router and devices bypasses CGNAT entirely for IPv6-capable destinations. Many modern websites, streaming services, and cloud platforms now support IPv6.

Use a VPN or proxy with port forwarding. Some VPN providers offer dedicated IP addresses or port forwarding features that bypass CGNAT limitations. Your traffic exits through the VPN provider’s infrastructure, which holds public IPs. This approach restores port forwarding and peer-to-peer functionality, though it adds a hop to your connection.

Switch ISPs. In competitive markets, some providers advertise “public IP included” as a selling point. If your current ISP refuses to offer one and CGNAT causes ongoing problems, switching may be the cleanest solution. Check provider forums and comparison sites to see which ISPs in your area still assign public IPv4 addresses.

Run services in the cloud. If your goal is to host a website, game server, or remote access point, hosting it on a virtual private server (VPS) avoids the CGNAT problem entirely. You access the cloud instance over its public IP, and the server remains reachable from anywhere.

What to Do Now

Start by checking whether CGNAT affects you. Compare your router’s WAN IP with the result from an external lookup. If your WAN IP starts with 100.64 through 100.127, or any other private range, your ISP has placed you behind CGNAT.

Once you know your status, decide whether it matters for your use case. Casual browsing and streaming work fine. Online gaming, self-hosting, and some remote work setups may require action. If you need a public IP, call your ISP and ask about their policy. If they will not provide one, evaluate a VPN with port forwarding or a switch to IPv6.

Your IP address is no longer guaranteed to be unique. Understanding CGNAT helps you diagnose connection problems and choose the right fix.

For more on how ISPs manage addresses, read our guide on how ISPs assign IP addresses. To understand the difference between address types, see our comparison of static and dynamic IP addresses. If you are new to IP addressing, start with what is an IP address.