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How to fix and resolve double NAT issues on your business network

Network & Internet KB-284

Summary

This guide helps you troubleshoot and resolve: How to fix and resolve double NAT issues on your business network. Follow the steps below to fix the issue.

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Common Causes

Double NAT happens when two devices on your network are both performing Network Address Translation (NAT) at the same time. This is a common issue in small business and home office setups, particularly when a modem/router supplied by your internet provider is connected to a secondary router you have added yourself. While the internet may appear to work, double NAT can cause problems with VPNs, remote desktop sessions, online gaming, VoIP calls, port forwarding, and certain cloud applications. This guide will help you identify whether double NAT is affecting your network and walk you through resolving it.

Symptoms of Double NAT

Before making changes, confirm that double NAT is likely the cause of your issues. Common symptoms include:

A quick way to check is to log into both routers and compare the WAN/internet IP address shown on each. If the secondary router's WAN address is a private IP (such as 192.168.0.x or 10.0.0.x) rather than a public address, you have double NAT.

Quick Fix Overview

There are two reliable ways to resolve double NAT. Choose the option that best suits your equipment:

  1. Bridge the primary modem/router so it passes the public IP straight through to your secondary router, which then handles all routing and NAT.
  2. Disable NAT on the secondary router and let the primary modem/router perform all routing functions.

For most small business networks, Option 1 (bridge mode) is the preferred approach because it keeps your secondary router in control of your local network features such as Wi-Fi, firewall rules, and DHCP.

Option 1: Put Your Modem/Router into Bridge Mode

Before You Begin

Step-by-Step Instructions

  1. Connect a computer to the primary modem/router using an Ethernet cable, or join its Wi-Fi network.
  2. Open a web browser and type the router's gateway IP address into the address bar. Press Enter.
  3. Log in with the router's admin username and password.
  4. Navigate to the internet, WAN, or connection settings. The exact menu name varies by manufacturer. Look for sections labelled Internet, WAN, Connection Type, or Network Mode.
  5. Change the operating mode from Router or Gateway to Bridge Mode. Some devices call this IPoE Bridge, Transparent Bridging, or Modem Only Mode.
  6. Save the changes. The router may reboot automatically.
  7. Reconnect your computer directly to the secondary router and verify that its WAN IP address is now a public IP rather than a private one.
Putting a modem/router into bridge mode disables its Wi-Fi, DHCP, and firewall features. Make sure your secondary router is configured and ready before making this change, or you may lose internet access on all devices.

Common Vendor Paths

If your ISP-locked modem does not expose a bridge mode option, you may need to contact your internet provider to request it, or proceed with Option 2 instead.

Option 2: Disable NAT on the Secondary Router

Use this option when you cannot put the primary modem into bridge mode, such as with some ISP-supplied locked devices.

Step-by-Step Instructions

  1. Connect a computer to the secondary router via Ethernet or Wi-Fi.
  2. Open a web browser and enter the secondary router's gateway IP address.
  3. Log in with the admin credentials.
  4. Navigate to the Advanced, Firewall, or NAT settings.
  5. Disable NAT. Depending on the router, this may be labelled NAT Filtering, NAT Boost, or Hardware NAT. Some routers require you to switch the operating mode to Access Point Mode or Wireless Access Point instead.
  6. Save the settings and allow the router to reboot.
  7. Confirm that devices connected to the secondary router can access the internet and that the WAN IP shown on the primary router matches a public IP address.
When using Access Point mode, the secondary router will no longer assign IP addresses. Make sure the primary modem/router's DHCP server is enabled and has enough address space for all of your devices.

Verifying the Fix

After applying either option, confirm that double NAT has been resolved:

  1. From a device on your network, visit a site such as whatismyip.com and note the public IP address shown.
  2. Log into your primary modem/router and compare the WAN IP address. They should match.
  3. Test the service that was previously failing, such as your VPN connection, remote desktop session, or VoIP call.
  4. From a computer, run tracert 8.8.8.8 in Command Prompt or Terminal. You should see only one hop before reaching your ISP's network, not two private router hops in a row.

Troubleshooting

The bridge mode option is missing on my modem

Some ISP-supplied modems lock this setting. Check whether your ISP provides a separate login or a companion app that exposes bridge mode. If not, use Option 2 or contact your ISP to confirm whether bridge mode is available on your plan.

I lost internet access after switching modes

VPN still will not connect

Double NAT may not be the only cause. Check that the VPN client is configured for your network and that no firewall rules are blocking the required ports. For ongoing issues, contact your VPN provider or network administrator for further assistance.

VoIP or gaming still has issues

If voice or gaming problems persist after resolving double NAT, check for QoS (Quality of Service) settings on your router and ensure firmware is up to date. Some applications also require specific ports to be forwarded on your secondary router.

Still Having Issues?

Need more help? If the issue persists after trying these steps, please open a support ticket and our team will assist you.

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