CGNAT Gaming Solutions

What is CGNAT?

Carrier-Grade NAT (CGNAT), also known as Large-Scale NAT (LSN) or NAT444, is a technique used by Internet Service Providers to conserve IPv4 addresses. Instead of giving each customer a unique public IP address, the ISP places multiple customers behind a single shared public IP.

Think of it like an apartment building: instead of each unit having its own street address, everyone shares one building address. The ISP's NAT device acts as a "front desk" that routes traffic to the correct apartment (your home network).

Why ISPs use CGNAT:

• •IPv4 addresses are exhausted (only ~4.3 billion exist)
• •It's cheaper than deploying full IPv6 infrastructure
• •Mobile carriers almost universally use it
• •Some residential ISPs have adopted it due to address shortages

How to Detect CGNAT

Not sure if you're behind CGNAT? Here are three reliable methods:

Method 1: Compare Your Router IP to External IP

Method 2: Look for CGNAT IP Ranges

If your router's WAN IP falls into these ranges, you're definitely behind CGNAT:

Method 3: Traceroute Test

Run a traceroute to any public server. If you see multiple private IP hops before reaching the public internet, you're behind CGNAT.

# Windows
tracert 8.8.8.8

# macOS/Linux
traceroute 8.8.8.8

Why Port Forwarding Fails with CGNAT

Traditional port forwarding requires you to configure your router to send incoming traffic on specific ports to your gaming PC. But with CGNAT, there are two problems:

Problem 1: Double NAT

Your game traffic now has to pass through two NAT devices:

1. •Your home router (which you control)
2. •The ISP's CGNAT device (which you don't control)

Even if you set up perfect port forwarding on your router, the ISP's CGNAT won't forward those ports to you.

Problem 2: Shared Public IP

The public IP shown to other players isn't yours alone—it's shared with potentially hundreds of other customers. There's no way for incoming connections to reach you specifically.

Problem 3: No Static IP Option

Many ISPs using CGNAT don't offer static IP addresses, or charge premium prices for a dedicated public IPv4 (often $10-30/month extra).

How MoleTun Solves CGNAT

MoleTun uses advanced NAT traversal techniques to establish direct peer-to-peer connections even through CGNAT. Here's how:

NAT Hole Punching

Instead of waiting for incoming connections (which CGNAT blocks), MoleTun makes both players initiate outbound connections simultaneously:

1. •Coordination: Both players connect to MoleTun's STUN/coordination server
2. •Discovery: The server identifies each player's external IP and port mapping
3. •Timing: Both players are instructed to send packets to each other at the same time
4. •Hole Punch: These outbound packets "punch holes" through both NAT devices
5. •Direct Connection: The NATs now recognize the connection as valid bidirectional traffic

This works because NAT devices (including CGNAT) allow outbound connections and their responses—they just block unsolicited inbound traffic.

Fallback Relay

For the rare cases where NAT hole punching fails (symmetric NAT on both ends, or aggressive firewalls), MoleTun automatically routes traffic through low-latency relay servers:

Setting Up MoleTun for CGNAT

Optimizing CGNAT Gaming Performance

Even with MoleTun solving the connectivity issue, you can optimize performance:

For Best Results:

• •Use a wired ethernet connection instead of WiFi
• •Close bandwidth-heavy applications (streaming, downloads)
• •If relayed, try gaming during off-peak hours when the relay has less load

If Connection is Unstable:

• •Your ISP's CGNAT device may be overloaded—try at different times
• •Switch to mobile data temporarily to test if it's an ISP issue
• •Contact your ISP about dedicated IP options if problems persist

CGNAT vs Double NAT

These terms are often confused:

MoleTun works in all three scenarios without any special configuration.