Adding a backup Internet WAN on my OPNsense Router

Jul 23, 2026

AKA "Spectrum has gone down two weeks in a row and I'm sick of it".

I've been borrowing a portable 5G gateway from my Dad for a few weeks, for testing... and two weeks in a row, I've used it as a backup Internet option, since my Spectrum Business cable Internet has gone down.

Spectrum Business Cable Modem offline

And yes, I'd get AT&T Fiber if I had the option, sadly they don't yet provide service at my studio. So I'm stuck with only one high speed wired provider. I may add on my own 5G backup Internet connection in the future, but we're getting off track.

The first outage, I unplugged my Cable modem from my ETH1 port, and plugged in the 5G gateway. I then rebooted the router, and also my main Mac (it's DHCP and DNS caching seems very aggressive, at least for Safari's networking stack).

That works, but it's quite inconvenient, because I had to keep checking on Spectrum's Internet status, then when it was finally back up, I had to walk back and re-plug my cable modem into my router, and reboot everything again.

Wouldn't it be easier if I could just... do it in software?

OPNsense and dual WAN

OPNsense router WAN2 port on back

My plan was to plug the 5G gateway into 'ETH2' (the third Ethernet port on my OPNsense box; ETH0 went to my LAN, ETH1 was for the Cable modem, and ETH2 and ETH3 are available—all are 2.5 Gbps ports).

'ETH2' was device 'igc2', so I logged into OPNsense, and under Interfaces > Assignments, I assigned new interface 'igc2' named 'WAN2'.

OPNsense Interface igc2 assignment

Then I clicked on WAN2 in the sidebar, and changed the following settings:

  • Enable (checked)
  • IPv4 Configuration Type: DHCP

Click 'Save', then 'Apply Changes' (at the top), then go to System > Gateways > Configuration, and make sure your new WAN2 gateway has appeared there.

(Since I don't want automatic failover, I won't set up any specific rules / monitors here, but you can figure that out on your own if you want that.)

Go to Firewall > NAT > Outbound and make sure you have 'Automatic outbound NAT' set up. If it is not set up, you may need to add a rule for the WAN2 interface.

Failover

OPNsense Interface Gateway configuration page

To actually failover to WAN2:

  1. Visit System > Gateways > Configuration
  2. Edit WAN2_DHCP, and set the Priority to "1" (and make sure it is not 'Disabled')
  3. Edit WAN_DHCP, and set the Priority to "2"
  4. Click 'Apply' and wait a few seconds

I usually use curl icanhazip.com or visit fast.com to determine which connection my computer's actually using at any given moment.

To switch back, set WAN2_DHCP to "2" (or more), and WAN_DHCP to "1" (making sure it is not 'Disabled'), and click 'Apply' again.

Further reading: