How To: Set Up A Cellular-Backed Highly Available Home Internet Connection

An owned hardware solution for setting up ISP connectivity with cellular failover for high availability home networking setups

Daniel Rosehill
8 min readSep 13, 2021

If you’re interested in improving the stability of your home internet network, then you might have considered provisioning an internet connection that takes advantage of multiple connectivity sources.

Typically, these kind of setups are the preserve of businesses. However:

a) With so many of us working from home, the lines between business and home users are becoming increasingly blurry.

b) With so many of us working from home, bandwidth demands on home connectivity are in many localities at a stretching point. This poses a problem because even some home-based business users require connectivity that is more reliable than what their ISP — or ISPs in their area — are capable of supplying.

The finished first part of the home networking stack. Bottom: ISP router. Middle: load balancing router. Top: cellular router. Photo: author.

ISPs commonly provide routers to customers in order to easily connect them to their networks. However, for many home internet users, owning their own hardware is preferable.

Purchasing hardware downstream of the modem level also has its benefits (your ISP’s router can typically still be used to bridge their connectivity / as a modem only). Assuming your downstream hardware doesn’t create a bottleneck for the super fast connectivity upstream, you can change ISPs and still use your system.

Here’s a method that I’ve used to achieve cellular-backup internet in Israel. I’m by no means suggesting that this is the best method of achieving this. In fact, I know for certain that there are more elegant ways to achieve this setup with less hardware.

However, I built this system with a reasonably small budget — and chose the components that could do what I needed at the least overhead. If that’s your situation, you might find these steps useful.

Purchase A Load Balancing Router

The cornerstone of this setup is our load balancing router.

We’re going to require one that offers failover. Which means that when connection A drops (our ISP line) connectivity automatically flips over to our cellular line.

Note: there’s a lot of confusion out there between failover, load balancing and bonding.

  • Bonding is that fancy technology that allows you to combine the connectivity from multiple providers into one fancy and super-fast connectivity trunk. Unfortunately — and as I learned recently — you need bonding on the WAN side of the network too. Speedify provides a cost-effective alternative to using hardware. If you’re into open source, check out the OPENMPTCProuter project.
  • Load balancing is used all the time in server-land to balance incoming connections between a variety of servers. In home networking, it works the same but in reverse. Your local devices are trying to access the (outside) internet and the load balancer will route them to the best internet connection (WAN) for their needs. Load balancers typically support various modes of operation.
  • Failover is the simplest of the three. As above, it simply means that when connection A goes down the load balancing router will flip over to WAN 2. If you have three WANs, you can configure failover to WAN 3 if WANs 1 and 2 both go down.

The majority of load balancing routers you’ll be able to find will do both failover and load balancing. For bonding, you’ll need to do a lot more legwork.

Final recommendation? Before purchasing your load balancer, pay attention to what connectivity you have currently in place and how fast it is. Some — like many of the Draytek load balancing routers — have built-in modems. You can find options that will support VDSL2 too. As well, of course, as built-in cellular.

Why does the maximum speed the WAN ports can carry matter? Because if you have a fiber optic connection that typically pulls in a 300 Mbps download speed you won’t want to put that into a load balancing router that can only pass through 100 Mbps on any of its RJ45 ports. None of the hardware you’re purchasing should be a bottleneck for what’s upstream of it on your network.

Note: you can simplify this setup by purchasing a load balancing router that either has an embedded SIM module or which supports USB plug-in dongles.

Buy A Data SIM And A Cellular Router (Or Choose A Cellular-Capable Load Balancer)

Fortunately, where I’m based, data only SIM plans have come down a lot in price.

I’m currently paying not even $10 a month for a 4G/LTE capable SIM that lives in my cellular router.

At the time of writing, 5G routers are significantly more expensive than their 4G counterparts. 5G-capable data plans will typically cost more too.

Pay attention, again, to compatibility.

If you’re planning on going with a load balancing router that can support cellular on the device (in some ways preferable) then check to make sure what frequencies it supports and compare those with the ones your network of choice uses.

The same goes for cellular routers: if you’re buying one then make sure it can support your frequencies too.

There’s one pro for buying a load balancer with cellular capability to mention and one negative.

The pro is that it’s going to cut down on the hardware devices we need by one component. The con is that it’s going to be driving our cellular connection straight into the load balancer.

If we keep cellular on its own hardware, this actually gives us a little bit more versatility. For instance, I can both run the cellular router into the load balancer and run it into my computer by WiFi. The latter will allow me to use a tool like WiFi to bond my home internet connection that already has built-in cellular backup.

Set Up And Connect Your Hardware

Firstly, you’re going to want to configure your ISP router, if possible, as a bridge.

Effectively, we want to use its modem and not its routing. So we’ll want to disable the DHCP server too (note: sometimes this makes it difficult to access the embedded web server. I’ve had success with this setup while leaving the DHCP server untouched). We’ll also want to set the cellular router to have an IP address that’s outside the IP address range of the LAN.

Of course, you may also use a load balancer with the requisite built-in modem and forego using the ISP hardware altogether. But sometimes it makes sense to keep this in order to keep the ISP and technicians happy and willing to provide support if you need help diagnosing why the ISP line is down.

We’ll want to repeat that process with the cellular hardware. Again, we want it to work as a cellular bridge and bridge that connectivity into the load balancer.

Note: for the TP-Link product I purchased, I needed to follow a workaround from the community forums. You can get around that problem by just buying an LTE/cellular modem that explicitly says it will work just as a modem/bridge.

Disabling the DHCP server on a TP-Link cellular modem/router. Photo: author.

Once we have the ISP and cellular routers both running as bridges, we can set up the load balancer and connect them into the WAN ports.

Layer one of the routing stack with the IP router (below) and the TP Link load balancer (above). Photo: author.
Layer two of the routing stack with the IP router at bottom, the load balancer in the middle, and the cellular router on top. Photo: author.

The photos above show the first part of my hardware stack.

Because I wanted to transmit WiFi from another room, I’m also running a LAN cable out of the load balancer and using that to drive connectivity to a WiFi router (another TP-Link product) that is running in access point (AP) mode.

Here’s how my current setup looks like on a diagram:

Configure Backup / Failover In The Load Balancer

If all goes smoothly, you should now be bringing two internet connectivity sources into your load balancer which is effectively providing routing for your whole network.

Now you’ll just want to make sure that the load balancing appliance is configured to handle failover so that when WAN 1 goes down (say, your ISP) WAN 2 will come up (say, your cellular router).

I configured my backup rule like this:

Suggested Additional Improvements

  • If you’ve gone to this much trouble you should consider putting all your networking equipment on an uninterruptible power supply (UPS) so that the whole stack can keep running during power outages or survive momentary blips without losing connectivity.
  • Finally if you’re using a cellular router with external antenna support consider that where you’re locating the networking stack mightn’t be the best place from which to pick up cellular connectivity. SMA extenders are cheap and you could run in connectivity from wherever is best in the house (or an external dish).

How Well Does Failover Work Using This Implementation?

I initially didn’t succeed in getting my TP-Link cellular router to work as a wireless bridge and pass connectivity into the load balancer.

So instead I ran my ISP internet directly into the device and configured the cellular network to only be used as backup connectivity.

Using that implementation, I experienced failover times of between 20 to 30 seconds.

Passing the two devices through the load balancer has resulted in substantially quicker failover — of about 2 seconds or so. This I imagine is because the cellular connection is always “live” and waiting to be used. In the first implementation the cellular router had to first “wait” for the outage, then bring up cellular, and then fail over.

Why Not Use Your ISP Router And A Plug In Modem?

  • This setup allows you to own your own hardware.
  • This setup also allows you to move your setup to different connectivity sources assuming that the downstream hardware doesn’t create a bottleneck.

Why Not Just Use A MiFi / Hotspot?

  • This setup is always online and live
  • Failover from ISP to cellular and back takes place completely automatically with this setup.
  • This setup brings the enhanced dual connectivity to every device on the network, including both wired and wireless endpoints.

Some Ideas For Alternative Implementations



Daniel Rosehill

Daytime: writing for other people. Nighttime: writing for me. Or the other way round. Enjoys: Linux, tech, beer, random things.