Why it matters more now
When email, files, phones and line-of-business apps all live in the cloud, an internet outage stops the whole office. One backhoe on the block, one failed piece of equipment in the basement, and nobody can work.
Your backup options
| Option | Strengths | Watch out for |
|---|---|---|
| Second wired line (fiber or cable) | Full speed, low latency | Same provider or same conduit means one cut takes both down |
| Fixed wireless | Different physical path from wired lines | Needs line of sight; availability varies by building |
| 5G / LTE cellular | Fast to install, no wiring into the building | Signal inside the building; data caps on some plans |
The best backup shares as little as possible with the primary: different provider, different cable route into the building, ideally a different technology.
How dual-WAN failover works
Your firewall connects to both lines and constantly checks whether each one can reach the internet. When the primary fails, it moves traffic to the backup, usually within seconds. When the primary recovers, it moves back.
Calls and video meetings may drop and reconnect at the moment of failover. SD-WAN goes further: it measures quality on both lines continuously and can move voice and video away from a line that's degrading, not just one that's down.
Checklist so the backup actually works
- Confirm the two lines enter the building by different routes.
- Put the firewall, switches and the backup modem on a UPS.
- Set up health checks against real internet destinations, not just the provider's gateway.
- Make sure inbound services, such as remote access VPN, still work on the backup line.
- Test failover by unplugging the primary, during business hours, once a quarter.
- Get alerts when the office is running on backup, so a dead primary doesn't go unnoticed for weeks.
Both FortiGate and Meraki MX firewalls support dual-WAN failover and SD-WAN.
