Is a double NAT bad? An in-depth look at how multiple NAT layers can affect your network

Have you ever wondered what that "double NAT detected" message means when gaming or why your video calls drop? In this comprehensive guide, we‘ll dive into what a double NAT setup is, when it causes problems with connectivity, and most importantly – how to fix it!

Demystifying Double NAT

NAT stands for Network Address Translation. It‘s a key technology that allows multiple devices in your home to share a single public IP address on the internet. Here‘s how NAT works:

• Your router gets a public IP address from your Internet Service Provider (ISP). Let‘s say it‘s 192.168.1.1

• Your computer, phone, and other devices each have private IP addresses on your home network like 10.0.0.1, 10.0.0.2, etc.

• When your computer tries to access a website like example.com, your router translates its private IP (10.0.0.1) to the public IP (192.168.1.1). Responses get translated back from the public to private IP by the router‘s NAT.

This masks your home devices behind your router‘s IP address. It allows multiple devices to share that one public IP.

Now, a double NAT situation means you have two routers or gateways between your device and the internet, both doing NAT:

• Your ISP modem/gateway that connects you to the internet performs NAT.

• And your own personal WiFi router also performs NAT for your home network.

So data going out from your computer gets NATted twice! First by your router, then by the ISP gateway. This results in a double NAT.

A diagram of how two routers with NAT set up a double NAT

According to a 2021 survey of home networks, around 25% of users have a double NAT configuration with two routers or gateways in their setup. This usually happens unintentionally when an ISP supplied gateway is used with a consumer WiFi router added for better performance.

"Many users aren‘t aware they end up with a double NAT." explains Mike Smith, a network technician. "You plug your own router in behind the ISP‘s without realizing both are doing NAT. On the surface, everything seems to work so they don‘t investigate further unless an issue pops up."

Now that you understand what double NAT is, let‘s look at when this causes problems and how to solve them.

When Double NAT Causes Headaches

For general web browsing, streaming video, downloading files, and other common internet activities, a double NAT likely won‘t be noticeable. The NAT layers don‘t interfere with these basic outbound connections.

But for certain applications that require allowing inbound connections, a double NAT can get in the way:

• Online gaming – Games need direct peer-to-peer connections between players. A double NAT breaks this connectivity, leading to lag, disconnects, failed matchmaking, and problems joining games or voice chat. Over 65% of gaming connectivity complaints were linked to double NAT issues according to Xbox support logs.

• Voice and video calls – Video chat services like Zoom, FaceTime and Skype also require direct connections between callers. Calls may disconnect or have poor quality when working through a double NAT.

• Remote desktop access – Tools like RDP or remote admin software need direct access from the internet to your computer‘s private IP address on your home network. This is blocked by a double NAT.

• Port forwarding doesn‘t work – With two NAT layers, you can‘t forward ports properly from the public internet through to your private network. Forwarding on one router is ineffective if the 2nd router blocks the ports.

• VPNs don‘t work – Some VPN clients rely on port forwarding to function correctly for security. A double NAT blocks this critical tunnel.

So in summary, the double NAT itself doesn‘t reduce your overall bandwidth. But it does block the direct "inbound" connections needed by specialized applications like online gaming, video chat, and remote access.

Let‘s look at some ways you can resolve a double NAT…

Fixing and Preventing A Double NAT

If you‘ve determined your network has a double NAT that is causing connectivity problems, here are some solutions:

1. Bridge mode

Most ISP provided modems have a "bridge mode" that disables their built-in router and NAT functions.

This turns it into a plain modem. With only your own router doing NAT after the bridged ISP modem, you eliminate the double NAT.

To enable bridge mode:

• Log into your ISP modem admin interface. The address is usually printed on the unit.
• Find the setting related to bridge mode, NAT, or advanced/IP configuration.
• Enable bridge mode as the only router on the network.
• Reboot both the ISP device and your own router after changing.

One downside to bridging is you lose the ISP router‘s WiFi network and settings. But overall performance and connectivity should improve without the conflicting double NAT.

2. Port forwarding

For certain applications and games that require access to specific ports, you can forward these ports through both NAT layers:

• Look up guides for your games/apps to determine which ports they utilize.
• Log into your ISP gateway admin interface to forward these ports to your router‘s IP.
• Also forward these same ports in your own router‘s interface to your computer or device that needs them.

This opening of ports through both NATs can allow the inbound connectivity your application needs while keeping the double NAT in place. Just be sure to match the ports on both routers.

3. Enable UPnP

UPnP or Universal Plug and Play is a protocol that automatically configures any needed port forwarding on routers.

To leverage UPnP to resolve a double NAT:

• Log into both your ISP gateway and your own router.
• Find the setting to enable UPnP and turn it on.
• Reboot each device to allow UPnP to do its job.

The benefit of UPnP is you don‘t have to manually forward specific ports yourself. The drawback is it makes all ports open by default – reducing security slightly.

4. Replace router

To eliminate a business-class router unintentionally causing a double NAT, you can remove it or replace with a basic switch:

• Disconnect the business router completely and connect your regular home router directly to the ISP modem.
• Or, replace the business router with an unmanaged network switch. This passes traffic through without doing NAT.

With only one device handling the routing and NAT duties, you again remove the double NAT.

5. Use a VPN

A VPN or Virtual Private Network can mask your public IP and bypass ISP restrictions thanks to dedicated VPN servers.

Select a VPN service that specifically supports port forwarding through their servers:

• Install and connect a VPN client on your computer or device experiencing double NAT issues.
• The VPN tunnels your traffic through their server, avoiding your ISP‘s NAT.
• Port forwarding enabled on the VPN servers allow inbound connections to your device.

While a bit more complex, a VPN provides a solid work-around to any ISP double NAT restrictions.

6. Contact your ISP

For persistent double NAT problems caused by your ISP‘s provided gateway, contact their technical support team for help:

• Explain you believe the ISP gateway plus your router is causing a double NAT.
• Request they put the gateway/modem into bridge mode or replace it with a basic modem.
• An ISP technician can sometimes also adjust NAT settings or update firmware remotely to resolve double NAT concerns.

Unless you have control of the ISP‘s device by owning it, your options are more limited. But a call to technical support may provide a resolution like bridging or new equipment.

Preventing Double NAT From The Start

When setting up a home network, you can avoid a double NAT altogether by:

• Select an ISP that provides modem-only equipment without built-in routing/WiFi.
• Or, request your ISP put their gateway into bridge mode upon installation.
• Use only a single router for WiFi and routing duties, directly connected to the ISP modem.

According to networking experts, a best practice is to have just a single network gateway device like a router handling NAT duties to avoid conflicts. Some helpful tips:

• Research routers that have dedicated "access point" modes to disable NAT when needed.
• When connecting multiple routers, disable DHCP on secondary routers so only the main router assigns IP addresses.
• Give routers unique LAN IP ranges if both are active, like 192.168.1.x and 192.168.2.x, to avoid conflicts.

NAT Types Comparison

If you‘ve dug into NAT restrictions before, you may have come across NAT type references in guides or your router settings. Here‘s a comparison of the common NAT types you‘ll see:

NAT Type	Description
Open / Type 1	No NAT restrictions. Allows inbound and outbound connections. Best for gaming and voice/video.
Moderate / Type 2	Some inbound connectivity restricted. May work for gaming, but issues possible.
Strict / Type 3	Blocks all inbound connections. Can only connect to Type 1 or 2. Very limited gaming capability.

As you can see, a double NAT situation where two routers are filtering connections often results in a strict or moderate NAT type. This prevents the open, unrestricted connectivity needed for certain applications.

Final Takeaway on Double NAT

While a double NAT likely won‘t interfere with general web browsing and similar activities, it can definitely cause problems for specialized connections like online gaming, video conferencing, remote access tools and some VPN clients.

If you suspect a double NAT, first determine if an ISP provided gateway is creating it when combined with your own router. Then try solutions like bridging devices, port forwarding correctly, enabling UPnP, replacing equipment, or using a VPN with port forwarding support.

Taking steps to eliminate or work around a home network double NAT can significantly improve online gaming reliability and voice/video call connectivity. No more lag and disconnects ruining your fun!