Using an LTE backup to get around an unstable cable modem connection

A graph of packet loss showing 10–20% over the space of a few hours.
packet loss spanning a few hours in the morning
A graph showing 4–5 hours of severe latency on a home network
latency storm spanning many hours in the afternoon

Using LTE as a backup link

  1. A network appliance that can aggregate multiple WAN links into a single logical connection for the home LAN
  2. An LTE data-capable SIM
  3. Something to act as an LTE modem

Multi-WAN capable gateway

The Protectli 4-Port Vault Appliance

LTE network gateway

The Protectli 4G LTE Modem

Google Fi Data Sim

  1. reasonable per-GB pricing
  2. no/low monthly fee
  3. no need to manually “top up” your account to get more data


  1. Plug your home network (I use eero) into the LAN side of the network firewall appliance. This will create a double-NAT situation — make sure that the DHCP network that the network appliance uses is distinct from the IP addressing inside your home network. Many home networks use As an example, you could set up the DHCP range in on the network appliance to be
  2. Plug in one WAN interface to your cable modem, plug in the LTE modem into a second interface (often labelled OPT). You’ll want to make sure to use yet another distinct DHCP range for the LTE modem to manage — it will be handing out an address to your network appliance to use.
  3. In your firewall software, configure a gateway group and tailor the latency and packet loss metrics to get the right level of responsiveness.
Gateway group configuration.

How does it perform?

  • Things still fuzz out on video calls, as it can take longer than you want to get it to switch.
  • Conversely, you can make it too sensitive and have it switch too often — and every switch is experienced as connections dying and timing out.
  • Persistent connections (like Slack’s websockets) can get unhappy when the gateway switches and can require a restart/reload.




Senior Software Engineer and blogger at Palantir Technologies (@PalantirTech) I used to be named Ari Gordon-Schlosberg; an explanation:

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Ari Gesher

Ari Gesher

Senior Software Engineer and blogger at Palantir Technologies (@PalantirTech) I used to be named Ari Gordon-Schlosberg; an explanation:

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