If you’ve ever noticed that your public IP address changes depending on what site you visit, or that you’re getting blocked or flagged on services for suspicious behavior, there’s a good chance you’re experiencing the effects of Carrier-Grade NAT (CGNAT) — a common networking technique used by mobile carriers like T-Mobile, Verizon, and AT&T.
In this article, we’ll break down what CGNAT is, why it’s used, and how it can affect your internet experience.
📦 What is CGNAT?
CGNAT, or Carrier-Grade Network Address Translation, is a method used by ISPs to allow multiple customers to share a single public IPv4 address. With IPv4 addresses running low, this is a practical solution to ensure everyone can access the internet.
In simple terms: It’s like sharing one public entrance to a building where each resident still has their own apartment — you all appear as the same person from the street, but you’re different individuals inside.
Key points:
- It’s commonly used on mobile and broadband networks to conserve IPv4 addresses.
- CGNAT = large-scale NAT: It places many users behind a shared public IP.
- Devices are assigned private IPs, and the ISP translates those to public IPs.
📱 How Mobile Carriers Use CGNAT
Mobile carriers deal with massive amounts of devices connecting and disconnecting constantly. Rather than assigning each device a public IP, they rely on CGNAT to manage traffic efficiently.
When you’re on a mobile data connection:
- Your device is given a private IP address.
- All internet-bound traffic is routed through carrier-owned NAT gateways.
- Your public IP may change frequently, even within a single session.
- Traffic is load-balanced across different NAT gateways behind the scenes.
This setup helps carriers efficiently serve millions of devices without exhausting IPv4 resources.
🔁 Why You See Different IPs
If you’ve ever used two different IP-checking websites and seen different IPs, CGNAT is likely the reason. This is a common (but confusing) side effect of how your mobile carrier routes traffic.
Here’s why this happens:
- Your traffic may pass through different CGNAT gateways depending on tower handoffs or load balancing.
- Different websites use different techniques (e.g., HTTP headers, DNS, TCP source IP) to detect your IP address.
- As a result, you may appear to have multiple public IPs even though you’re on the same device and network.
This is expected behavior on CGNAT-enabled networks and not something to worry about unless it interferes with specific services.
⚠️ Common Issues Caused by CGNAT
While CGNAT is a helpful solution for carriers, it introduces a few side effects that can disrupt how services interact with your device.
Some of the most common issues include:
- Inconsistent IP detection: Services relying on stable IPs may see your session as switching locations or users.
- Blocked services: Abuse by someone sharing your public IP may result in shared bans or rate-limiting.
- No port forwarding: Devices behind CGNAT can’t be accessed directly from the internet, which breaks remote access and hosting.
- Filtering issues: IP-based content filtering or parental controls may not work reliably due to dynamic IP assignment.
These issues can impact everything from VPNs and game servers to custom DNS filtering setups.
🧭 How to Work Around CGNAT
Although you can’t disable CGNAT on a mobile network, there are a few ways to improve consistency and reduce its impact on your experience.
Here are some potential workarounds:
- Use IPv6: If your carrier supports IPv6, it gives your device a unique global IP without NAT.
- Request a static IP: Some carriers offer business accounts or add-ons with a fixed public IP.
- Use a VPN: A VPN gives you a consistent external IP and bypasses CGNAT’s effects (but introduces new considerations).
- Switch to device- or hostname-based filtering: If using a DNS filtering service (like CleanBrowsing), avoid relying solely on public IP for policy enforcement.
These approaches can help maintain session stability and improve compatibility with certain services.
🌐 How CGNAT Affects DNS-Based Resolvers
DNS-based resolvers like CleanBrowsing, and others use public IP addresses to associate filtering policies with devices or networks. However, CGNAT introduces complications that can make these DNS services behave unpredictably — especially on mobile networks.
Because CGNAT hides individual devices behind shared public IPs and dynamically rotates them, several issues can arise that affect how DNS resolvers identify and apply policies:
- Public IP instability: Devices behind CGNAT often receive different public IPs over time. If your DNS filter ties policies to a specific IP, you may see inconsistent enforcement — sometimes the policy applies, sometimes it doesn’t.
- Shared IP collisions: Multiple users on the same CGNAT IP can inherit each other’s DNS rules, leading to misapplied filters or unfair blocks due to someone else’s behavior.
- Poor geolocation or routing: Since DNS resolvers may use the public IP to determine geographic location or nearest point of presence, CGNAT can lead to incorrect geolocation and slower resolution speeds.
- Encrypted DNS complications: Services that use DoH/DoT or try to enforce encryption by IP may struggle to enforce rules correctly when traffic is routed through shared or rapidly changing IPs.
These limitations make IP-based policy enforcement less reliable in CGNAT environments. To address this, we recommend shifting to device-based filtering, using DoH/DoT with unique tokens, or applying policies via authenticated clients instead of relying on public IPs.
CGNAT is a behind-the-scenes networking tool that helps mobile carriers scale their networks — but it can cause confusion for end users. If you see different public IPs or encounter weird access issues, CGNAT is likely the reason.
Key takeaways:
- CGNAT shares one public IP across many users.
- It causes dynamic IP changes and inconsistent behavior across services.
- It’s common on mobile networks and can’t be disabled by end users.
- Use IPv6 or VPNs to regain consistency where needed.