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Solutions for Resolving Double NAT with USG

  • Two solutions are proposed to resolve the double NAT issue with a USG in a network involving two different ISPs: load balancing the two connections with one ISP as the primary WAN and the other as the secondary WAN, and using a TP-Link load balancer to manage both ISPs.
  • The first solution, load balancing with the USG, can eliminate double NAT but poses a risk of service interruption if the primary connection goes down. Configuring a static IP and DMZ in the primary modem may enhance this setup.
  • The second solution introduces a TP-Link load balancer, potentially providing more reliable load balancing. However, it may have limitations on the number of supported devices. The choice between these solutions should be based on the network’s specific requirements and compatibility with existing configurations.

If you’re facing a double NAT issue with a high-speed modem router (modem 1) and a slower but configurable ISP modem (modem 2), here are two ideas to tackle this problem:

Idea 1: Load Balancing with USG

Consider making modem 2 your primary WAN connection on the USG, while using modem 1 as the secondary WAN. Load balance the two connections, distributing traffic, say 50% each. This setup can potentially eliminate the double NAT problem. However, be mindful of the following concerns:

  • If modem 2’s internet connection goes down, you’ll experience service interruption.
  • Using a static IP address for the USG and configuring DMZ in modem 2 can help, but ensure it’s compatible with dual WAN setup.

Idea 2: TP-Link Load Balancer

Alternatively, you can introduce a TP-Link load balancer like the R470t+ to manage both ISPs. Connect both modems to the load balancer and then connect the USG to the load balancer. This approach can work effectively. However, be aware of the R470t+’s limitation in providing IP addresses for more than 254 devices.

The choice between these ideas depends on your network’s specific requirements, tolerance for potential downtime, and the number of devices you need to support. Evaluate your options and their compatibility with your network configuration.


Resolving the double NAT issue with a USG involves considering two potential solutions. Idea 1 suggests configuring one ISP as the primary WAN and the other as the secondary WAN on the USG, employing load balancing to distribute traffic. However, this setup carries the risk of service interruption if the primary connection goes down. Idea 2 proposes using a TP-Link load balancer to manage both ISPs and connect the USG to it, providing a balanced and potentially more reliable solution, although it may have limitations regarding the number of supported devices.


The solutions presented here are general ideas to address the double NAT issue with a USG. Specific network configurations may vary, and it’s essential to consider your network’s unique requirements and constraints. These solutions may require technical expertise, and any changes made to your network should be approached with caution. Always consult with IT professionals or experts to ensure that the chosen solution aligns with your network’s needs and is implemented correctly.

Alex Lim is a certified IT Technical Support Architect with over 15 years of experience in designing, implementing, and troubleshooting complex IT systems and networks. He has worked for leading IT companies, such as Microsoft, IBM, and Cisco, providing technical support and solutions to clients across various industries and sectors. Alex has a bachelor’s degree in computer science from the National University of Singapore and a master’s degree in information security from the Massachusetts Institute of Technology. He is also the author of several best-selling books on IT technical support, such as The IT Technical Support Handbook and Troubleshooting IT Systems and Networks. Alex lives in Bandar, Johore, Malaysia with his wife and two chilrdren. You can reach him at [email protected] or follow him on Website | Twitter | Facebook

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