How to Best Use an Existing Router or (ISP-Provided) Gateway

A cable modem (left), a Wi-Fi router and a residential gateway.
Dong Ngo | Dong Knows Tech A cable modem (left), a Wi-Fi router, and a residential gateway.

Ideally, you should use just one router for your home network. But sometimes there’s no choice, like when you have to keep that ISP-provided gateway and yet want to expand or upgrade your system.

A gateway is a single hardware box that includes a Wi-Fi router and a modem on the inside. That said, within this post, a gateway is, first and foremost, a router.

This post helps you get the home network you want even when you can’t or do not want to replace the existing router or gateway. In the thick of it, it’s about how to use a router (or a mesh system) on top of another — a question of single NAT vs. double NAT.

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But depending on your situation, you might just need to do something as simple as making the most out of your gateway; or getting an access point or Wi-Fi extender.

In any case, before going further, make sure you’re comfortable with setting up a router.

How to configure an ISP-provided gateway properly

If you live in a small home, chances are the router you have at hand, likely it’s the gateway your Internet provider has installed, is enough for your Wi-Fi need.

In this case, you just need to configure it properly. There are a few things you should do. By the way, you can work on a gateway the same way you do a regular Wi-Fi router.

Change the default access to the gateway

All ISP-provided gateway comes with default admin access. For example, a Comcast gateway’s default password is almost always highspeed. As a result, almost anyone can log into its interface. For security, you should change this.

Dong Ngo | Dong Knows Tech It’s easy to change a Comcast gateway’s admin password via the link at the interface’s top right corner.

To do that, log in to the gateway’s web interface by pointing a browser to its IP address and log in with the default password (or access code). You can generally find this information on the side or bottom of the device.

Once you’ve logged in, navigate the interface to the area where you can change the password and create new one that’s more secure.

Make a meaningful Wi-Fi network

By default, each gateway has its own default Wi-Fi network of which both the name and password are hard to remember or type in, especially when you need to do that on a small screen or via a remote control.

You can give your Wi-Fi network a more meaningful name and a password that you can remember. You can use your name, but if you want to stay anonymous, you can pick anything. It’s the name that will appear as an available Wi-Fi network on a mobile device.

Again, you can do this via the web interface, and follow these guidelines to keep your system secure.

Customize your gateway

This part is optional, but most gateways have a decent set of features and settings that you can use — the amount varies from one device to another.

Examples of these include: port-forwarding, Dynamic DNS, separating the 2.4GHz Wi-Fi network from that of the 5GHz, and so on. Again, you can use the interface to customize these to your liking.

In short, just because you don’t use a standard router, doesn’t mean you can’t make your network with specific advanced settings. Dig into your gateway’s web interface; you might get surprised by how much you can get out of it.

Getting an extender or access point

If you live in a big home and the existing gateway doesn’t cover your entire home with Wi-Fi, it’s time to think about getting extra hardware to improve the coverage.

In this case, you need either an access point (AP) or a Wi-Fi extender. (Not sure which is which? Check out this post on APs and Extenders.)

Dong Ngo | Dong Knows Tech Many routers, like this Netgear RAX120, can work as a router, an Access Point, or a Client, and you can switch between the three using their web user interface (or mobile app.)

When to get an access point

Get an access point if you can run a long network cable (or a set of power-line adapters) from the gateway to it. You should think of this first since an AP delivers much better performance than an extender.

There are many options for APs, and most of them work similarly. Make sure you get one of the same or better Wi-Fi standards than that of the gateway.

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Also, note that most routers can work in AP mode. So if you have an old router, you can use it, too. More on this below.

Hint: You can make the AP’s Wi-Fi network share the same name and password as that of the existing router. In most cases, that’d give you somewhat of a mesh system.

The EX7500 (left) and EX8000 from Netgear are great choice for Wi-Fi extenders.
Dong Ngo | Dong Knows Tech The EX7500 (left) and EX8000 from Netgear are decent choices for Wi-Fi extenders.

When to get an extender

An extender can quickly extend your Wi-Fi, without you having to run a network cable.

Not all extenders are created equal, however. I’d recommend a tri-band one, such as Netgear EX8000 or Netgear EX7500. The reason is a tri-band extender uses one of this band as the dedicated link to the existing router. As a result, it will give you better Wi-Fi speed than a single or dual-band counterparts

Note, though, that using extender means you get the convenience at the expense of performance. Sometimes, the performance gets so bad; the convenience is not even worth it.

Generally, if you have fast Internet or want to use the Internet for real-time communication applications, such as Voice over IP or video conferencing, an extender won’t cut it. You’ll need to run network cables or at least get a mesh system.

Putting a router on top of your gateway: Double NAT vs. single NAT

This part means you get a Wi-Fi router, or mesh system, and use the existing gateway as though it were a modem.

In this case, the hardware setup part is easy. Connect the WAN (Internet) port of the router — or the primary router unit of your mesh — to a LAN port of the gateway (or the existing router).

Now configure your new router to our liking, and you’re all set. But it’s easy said than done. There are three things you need to keep in mind.

Different local IP address for each router

Your new router’s IP address must be different from that of the existing gateway. This address is often referred to as the “Default Gateway” IP, which is not related to the actual gateway. It’s quite rare that you have to worry about this, though.

That’s because chances are they are already different by default, and many routers are smart enough to automatically change its IP when it detects that the gateway already uses the same one.

Dong Ngo | Dong Knows Tech You can change the router’s IP, shown as the Default Gateway IP in the screenshot, via its web interface.

If, for some reason, the two share the same IP address, which tends to happen if the new router is from the same vendor as that of the existing one, among other things, you’ll note that devices connected to the new router won’t have Internet.

In any case, you can always change the router’s IP using the web interface. It’s in the LAN (or DHCP) area of the router’s interface. This IP tends to be in the form of 192.168.x.1 or 10.0.x.1. You just need to change x to a different digit.

With this out of the way, now you’ll have one out of two options, double NAT vs. single NAT.

What is NAT?

NAT stands for network address translation, which is a significant function of a router.

Among other things, it allows the router to use a single WAN IP address (provided by the ISP) to deliver Internet access to many devices connected to it. That said, each network needs just one router since by default a router always has its NAT turned on.

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Double NAT

Double NAT is when you connect one router to another and let them both function as routers.

Since a gateway is a router itself (plus a modem), when connecting another router to it, you’ll get a double NAT setup. Specifically, you have one NAT-enabled router running on top of another NAT-enabled router.

Dong Ngo | Dong Knows Tech In a double NAT, devices of private IP address set 1 can’t talk to those of private IP address set 2, and your router doesn’t connect to the Internet directly

Issues with double NAT

The primary problem with this setup is that devices belong to each NAT will not be able to communicate with one another locally. That because each router has its own private set of IP addresses.

For example, if you have a computer that connects to the gateway’s network, and a printer that connects to your new router’s network, the computer can’t print to the printer. The two just don’t “see” each other, at least not via their network names.

Another thing is advanced network settings, such as VPN, port-forwarding, etc. will not work as expected, if at all. 

Pro tips on using double NAT:

  • You can still use port-forwarding, but it takes more work. Specifically, you need to program that twice, first at the gateway, and then at the router.
  • To access the top-level NAT router’s interface over the Internet, set that up as a server port-forwarding entry at the first-level NAT (the gateway) — make sure the two use different ports for remote management.
  • A device of the upper-level NAT can still access one of the lower-level NAT if you use its IP address.

When double NAT works

If you just want to access the Internet, then a double-NAT setup will work out just fine.

Also, a double NAT setup makes the top-level NAT network — the one hosted by your new router — more secure. That’s because devices in this network are behind two layers of firewalls and NATs. They are also invisible to those connecting to the lower-level NAT, as mentioned above.

What to do in a double NAT setup

Now that you’re aware of double NAT and still want to use it, there’s just one thing you need to do: Turn off Wi-Fi on the gateway (you can do this via its web interface) and use only the Wi-Fi of your router. Alternatively, you can keep the gateway’s Wi-Fi network as a guest network.

After that, connect all of your wired devices to your router, and not the gateway, so that they can talk to one another locally. Then, mission accomplished.

Single NAT

As mentioned above, if you want to use advanced network features and all devices within your home to can talk to one another easily, it’s best to use the single NAT configuration. In this setup, your router connects directly to the Internet.

In this case, you have two options. Either you make the gateway forward the WAN IP address to your new router, effectively making it work as a modem, or you can turn your new router into an access point.

Dong Ngo | Dong Knows Tech In a single NAT setup, you have just one set of private IP addresses, and your router connect to the Internet directly.

Gateway-to-router WAN IP forward

Depending on the gateway you use, the configuration for this varies. With some, like cable gateways, you need to put the gateway in Bridge Mode, with others, like DSL gateways, you need to configure the IP Pass-through and map that to the local IP address of the router.

Again, the objective is to make your router has the WAN IP of the gateway, and not a local (private) IP given out by the gateway. In other words, the gateway now functions as a modem.

Another option is to use the DMZ or IP Passthrough setting of the gateway, if applicable, to forward all WAN requests to the router.

You can turn a Comcast Xfinity gateway into Bridge Mode using the web interface.
Dong Ngo | Dong Knows Tech You can turn a Comcast Xfinity gateway into Bridge Mode using the web interface.

And that’s it; you now will have a home network the same as one built with a modem and a router.

Turning your router into an Access Point

Most router and Wi-Fi systems can work as an access point. You can just log into their user interface and switch the operation mode into the AP mode. Note that in many routers and mesh systems, this mode is called “bridge mode,” which makes things a bit confusing.

Dong Ngo | Dong Knows Tech When in AP mode, your router (or mesh system) functions as the extension of the existing gateway and allows you to have a single NAT setup.

But generally, if you see a router that has three roles, router, AP, and bridge, then pick the AP mode. If you see only the first two, then the bridge mode is now likely meant to be the AP mode.

If your router does not have an AP mode, you can manually turn it into an AP mode by connecting it to the gateway using one of its LAN ports (and not its WAN port.)

By the way, you might want to configure the router’s Wi-Fi network before turning it it into an access point.

In the AP mode, the router — or a mesh system — will work only to extend the network and nothing else. You will not be able to take advantage of its other settings and features. In other words, your network only has the features and settings of the existing gateway (or router).

The takeaway

No matter what your Internet situation is, chances are you can still customize your home network to your liking.

In my experience, having to keep the ISP-provided gateway is the most popular situation, so the Gateway-to-router WAN IP forward section above is likely the most applicable to yours. It’s also relevant to most, if not all, Internet plans for a small business.

Dong’s note: I first published this piece on December 30, 2018, and updated it on April 13, 2020, with additional relevant information.

Ω Found a typo? Please report it by selecting the text and pressing Ctrl + Enter. Thank you! ❤️

19 thoughts on “How to Best Use an Existing Router or (ISP-Provided) Gateway”

  1. Dong,
    Here’s what I did:
    I configured a TPLink A6 as an AP and inserted between the ethternet drop and the Google mesh. Now they can connect to the A6 when they want to print. The signal does not reach all of the mesh area, but enough for them to use.

  2. I think we have to differntiate here. If the router is in WAN mode, its firewall is turned on and one cannot access (at least I cant, I cant even access the login interface of the router, since access from WAN is disabled), if it only NAT you can access… Agree?

    • You can only use a router as a router when it’s working as a router, D. A router can have different roles, some of which will turn it into something else that doesn’t have all the functions it can offer when working as a router.

  3. “A device of the upper-level NAT can still access one of the lower-level NAT if you use its IP address.”

    I am not sure – if this 100 % true? You have to use port forwarding though, typically the second router will block incoming traffic? I cant even ping my 2nd router from the first network…

    • Well, now you can be sure 100%, Nix. Try some Windows-based file sharing from a lower-level NAT device, you’ll be able to access the share via \\The-ip-address\ShareName from an upper-level NAT device. Fort forwarding has nothing to do with this.

      Or you can access the lower-NAT router’s web interface via its IP, from a upper-NAT device. That works.

  4. Dong,
    I live in a grandparents house next to the main house (about 40 yds apart). I have connect the houses with ethernet. Currently I run an asus rt86u in my house with wifi and ethernet connected devices including a printer. At the main house I have a 3 onhub google mesh. Everything works fine, but I would like to enable print to my printer from the mesh system. I thought I could enable ap mode on the onhub, but google says that it would not function as a mesh system. I have never used port-forwarding, but I am willing to try if that will work in my case. Do you have more details on port-forwarding?

    • It’s impossible with the current setup, Larry. That’s because the Google system doesn’t support the AP mode as a mesh system. What you can do is break up the Google system, and set up each of its hardware units as an AP (you can daisy-chain them) with the same Wi-Fi network (name and password) as that your RT-AC86U. That’s a bit of work, and you need to run cables to connect the units, but it will make both houses belong to a single NAT setup. More on that here. Everything will work as expected then.

  5. Great article Dong and very relevant for me. Question on double NAT. You say the local devices won’t be able to detect each other (since some may connect to modem/gateway and some may connect to another router), but your solution seems to solve that issue (disable gateway WiFi, connect only to the router). It’s not clear in the article that your solution solves some of the issues you mentioned with NAT.

    Would gaming features still work with this setup, or for gaming do you recommend setting the gateway to be strictly in “gateway” mode and pass that WAN IP to your own router? My current setup is AT&T gateway (default config) with several routers in AP mode connected to it. Wondering if this will hamper connections on PC and Xbox services/games. Thanks!

    • Cool, Ryan. Glad it applies. The gaming features of the router should work if you don’t have clients using the gateway. Otherwise, those might hog the Internet bandwidth before the outer. Basically, if you don’t use the gateway to serve clients, you’re fine. If you have multiple APs, make sure they connect to the router’s LAN ports, and not those of the gateway.

  6. Any insights on using single NAT on AT&T Fiber? I looked around gateway but could not locate AP or Bridge Mode at first glance.

    • Try to look for something like “IP Passthrough” or “Pinhole”, Luis. I’m not sure about the specifics which change depending on the particular modem but the idea is to pass the WAN IP to the router and believe you can do it with any AT&T modems (both DSL and Fiber). I’ve done this many times before.

  7. Thanks for responding so quickly Dong. Do you have any guides that are for setting up a moca? I tried searching on your site but didn’t find much. BTW i just found your website and i think its great! . I remember you from the CNET days. Sorry if this is too much of a request, i’m doing all the research I can and any advice is much appreciated.

    3 story town home; slim and tall 2k sq feet (probably 18 unit condo association surrounding me.
    Asus RT-86U
    It doesn’t seem to reach my 3rd floor as consistently as I’d like. Unfortunately I don’t think I can set up a wired Ethernet back haul. So i’m considering using moca: Hardware list below
    goCoax MoCA 2.5 adapters. qty 2 (1 for the modem and 1 for the AP) and splitters where needed
    $6 POE filter where coax comes into the house,
    Do you recommend what Asus AP to use in conjunction with the router for AI mesh.? alot of people on Reddit suggest TPlink EAP models, but i want to stay with Asus for AI MESH. As I tend to favor the asus brand.

    I’m also open scrapping what I have, upgrade to wifi 6 mesh products and use my old hardware for my parents house.
    I’m considering the ubiquiti alien +mesh and asus zenwifi systems. but they aren’t in stock due to covid19. Regardless for the mesh to work effectively I’d want MOCA installed anyways and want to make sure i’m setting it up correctly and just looking for any guides you know of.

    • MoCa is very straight forward for a single pair. You have two adapters at two ends of the cable and they will turn the cable into a network cable. Note though, in a home, you might not know where a cable begins and where it ends. Just because you see a cable outlet, doesn’t mean that outlet and the other one where you plug the OTHER MoCA adapter into are connected. If you want to do a MoCA network with multiple nodes, that can get complicated and it’s hard to troubleshoot since we tend to not know how the wires are run. Sometimes, they are even fragmented.

      I’d recommend running network cables instead. In the end, it might be easier than figuring MoCA out in your particular situation. 🙂

  8. Hi Dong, I noticed you don’t mention Moca as an alternative to wired Ethernet and power line when setting up an access point . Any particular reason ?

    • Good catch, Andrew! The reason is MoCA is only available in homes wired with coaxial cables. So it’s not something everyone can relate to. Powerline, on the other hand, is available in virtually all homes.

  9. Typically in Europe, replacing your ROUTER or ISP supplied device is either impossible or impractical without inside knowledge from an ISP worker. For example, at home in Switzerland, Swisscom supplies fibre routers with dumbed down resttriceted logon access and there are sophisticated Public/Private Key encryption keys which you have no access to preventing you simply replacing equipment even if you reverse Engineer the Fibre setting somehow. For Wingo NO logon access at all. What you can of course do, and is to be encouraged is to build an Infrastructure downstream of the ISP device, including an Independent chain of Firewalls, networks and Wifi Access points. And of course if you want to get serious, try Microtik.


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