Is Double NAT Bad?

Matthew Howard
Computer Hardware Engineer at - TechNab

Matthew Howard is a computer hardware engineer. After completing his graduation, he joined a renowned networking tools manufacturing company as an IT specialist and hardware...Read more

NAT stands for Network Address Translation, and it’s a way that routers use to translate addresses between different networks. But what happens if you have two routers doing this? You get a double NAT. But is double NAT bad?

Yes–Double Nat is bad because it can cause problems when trying to access certain services or websites. For example, if your router is translating addresses from your local network to the internet, but so is another router on another network (like your phone company), there could be conflicts that cause connections to fail.

So how do you fix a double NAT? Let’s take a deeper look at the problem and find out some solutions.

What Is Double NAT?

In computing terms, NAT means Network Address Translation. It’s a technology that assigns IP addresses to devices on a network. The most common use of NAT is to allow multiple devices on a single network to use the same IP address.

What Is Double NAT

For example, if you have a router at home and all your devices connect through that router, then the router does the work of assigning those devices unique IP addresses so they can communicate with each other.

Double NAT is when two different routers are assigned to do this job. This can happen when you have a router from your ISP, and then you also have a second router that you use for your home network.

The result is that some devices may appear offline or inaccessible from other devices on the same network—or even accessible from outside sources like websites or apps.

Is Double NAT Bad?

Yes, double NAT can be problematic for several reasons. When you have double NAT, it’s like having two people translating a conversation between two other people. It can cause problems because each router might be translating the addresses differently.

Is Double NAT Bad

This can cause communication problems between devices on the same network or even prevent certain kinds of communication from happening at all.

For example, you might not be able to access certain websites or services if your router is configured to use a different DNS server than the one provided by your ISP.

You might also have trouble using applications that require a specific port to be open. If one of the routers is blocking that port, the application won’t work. Here are some other potential problems you may encounter:

  • Disrupted Home Security System: Double NAT can cause problems with your home security system. If you have cameras or other devices that need to be accessible from outside your home, double NAT can prevent them from working.
  • Idling VoIP Services: It can also cause problems with VoIP (Voice over IP) services like Skype or FaceTime. If your router is configured to block certain ports, these services might not work.
  • Slower Internet Speeds: If your router is configured to use a different DNS server than the one provided by your ISP, it can cause slower internet speeds.
  • Difficulty Connecting to Gaming Servers: Double NAT can cause problems connecting to certain gaming servers if you play online games. For example, a double NAT can cause problems connecting to an Xbox Live server when using a wireless Xbox One console.
  • Difficulty Connecting to VPNs: If you use a VPN (a virtual private network), double NAT can cause problems with the connection. This is because the VPN needs to be able to route traffic through a specific port, and if one of the routers is blocking that port, the VPN won’t work.
  • Difficulty Connecting to Devices: If you have devices that need to be accessible from outside your network (like a printer or file server), double NAT can prevent them from being accessible.

How to Check a Double NAT?

You don’t immediately notice double NAT when you change ISPs. In fact, you might not even notice it until you run into one of the problems listed above.

One way to check if you have double NAT is to log into your router and check the WAN (wide area network) IP address. This is the address that your ISP assigned to your router.

How to Check a Double NAT

If this address is different from the one assigned to your computer, you likely have double NAT. Here are two more ways to check a double NAT.

Use canyouseeme.org

You can easily check for a double NAT by using the website canyouseeme.org. This website lets you check if a specific port is open on your network.

For example, if you want to check if port 80 is open, you would enter that into the website, and it would tell you if the port is open or not. If the port is closed, it could be because one of the routers is blocking it.

Use Command Prompt

You can also check for a double NAT by using the command prompt. To do this, open the command prompt and enter the following:

  1. On your OS, launch the command prompt.
  2. Run the following command: tracert 8.8.8.8 (Google DNS).
  3. Look for private IP addresses in the first two hops.

If both public and private IP addresses appear on the first two hops, you are running a single NAT. But you are running a double NAT if the first two hops return private IP addresses. For example, 172.16.0.1 or 192.168.1.10.

How to Fix a Double NAT?

Assuming that you have a Double NAT problem, here are some fixes you may want to consider before continuing to play online games or enjoy various services seamlessly.

1. Remove the ISP Router

The first and simplest thing you should try is disconnecting the ISP router from your network. Remove all cables between the router and other devices on your network, including computers, printers, NAS drives, etc. Then, connect everything to your preferred router directly. This will often be enough to fix your double nat issue.

2. Activate Your ISP Router’s Bridge Mode

If you’re not ready to let go of your ISP router, enabling the Bridge mode is your best bet. Bridge mode essentially turns off all of the gateway’s features and makes the router a dumb piece of hardware that just passes data from one device to another.

It does this by listening for incoming connections on one side (usually the WAN port) and sending those connections out through another (most often the LAN port). Here’s how you proceed:

  1. Access your router’s login page (located on the back or in the manual).
  2. Proceed by entering your credentials
  3. Navigate to Wireless Options (the option’s name may vary depending on your router).
  4. Toggle the bridge mode on or off
  5. Save your changes

If your router doesn’t have the toggle bridge mode option, you can try enabling your home router’s access point. This should also work. To do this, navigate to the Wireless Options shown above before doing the following.

  1. Enable or switch on access point mode
  2. Click the Save Changes button

3. Make Your Non-ISP router an Access Point

You don’t need to worry if your router does not support Bridge Mode. You can still make it work as a secondary access point. Here’s what you need to do:

1. Find Your Router’s IP and Subnet Mask

You need to find your router’s IP address and subnet mask first. To do this, open the command prompt and type “ipconfig.” Take note of the Default Gateway address. This is your router’s IP address. The Subnet Mask will usually be 255.255.255.0 unless you change it.

2. Tweak the DHCP Settings

Next, log in to your router and find the DHCP Settings page. Here, you will need to change the starting and ending IP addresses. The starting IP address should be one number higher than your router’s IP address. The ending IP address can be anything you want, but it’s generally best to make it the same as your router’s IP address.

3. Change the Router’s IP Address

Finally, you need to change your router’s IP address. To do this, log in to your router and find the page where you can change the IP address. Enter the new IP address and subnet mask that you noted earlier.

After making these changes, you should now be able to use your non-ISP router as a secondary access point and, thereby, disable the double NAT.

Conclusion

Hopefully, this article has given you a comprehensive insight into double NAT issues and answered ‘why is double NAT bad?’ as well as possible solutions to fix the problem.

As you can see, double NAT is a problem because it can cause laggy gameplay, slow internet speeds, and prevent you from accessing certain services. Besides, you may not even know if you’re having this issue before the troubles mentioned start appearing.

Yet, if you put a little effort into fixing the problem outlined here, you can enjoy seamless browsing online.

Matthew HowardComputer Hardware Engineer at - TechNab

Matthew Howard is a computer hardware engineer. After completing his graduation, he joined a renowned networking tools manufacturing company as an IT specialist and hardware technician.

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