Additional Observation:

After reboot, WAN1 (Comcast) becomes active correctly.

Several hours later, traffic is found to have migrated back to WAN2 (T-Mobile) without any known Comcast outage.

WAN1 still reports Online and maintains a valid public IP address.

This suggests either:

- a false failover event is occurring, or

- route selection is changing while both WANs remain healthy.

Additional Evidence from System Log

Example entries:

2026-08-05 07:18:09

The online detection result of [WAN1] was offline.

2026-08-05 07:18:32

The online detection result of [WAN1] was online.

WAN1 physical link remained connected and later recovered.

Observed behavior:

- Router fails over to WAN3 (T-Mobile).

- WAN1 subsequently returns online.

- Router does not automatically revert traffic to WAN1.

TP-Link support states that Online Detection cannot take effect if Load Balancing is disabled.

In my testing:

- Link Backup is enabled

- Load Balancing is disabled

- WAN1 offline/online events are recorded in the log

- Failover works

- Failback does not occur

Is automatic failback to the configured Primary WAN expected to require Load Balancing to be enabled?

  @JEJ3 Hi,

I have a very similar setup ... except that it's a T-Mobile G4AR. Some odd behaviour ... thoughts?

1) Config

- WAN2 is meant as backup, connected to LAN2 on the G4AR, because

- LAN3 is connected to the G4AR LAN1, it's supposed to be the online detection link (i.e. so Auto Backup can be enabled on the G4AR).

2) Observations / Issues

- I see in the thread setting 100:1 for the Load Balancing ... but also noting about turning it off? I can't see where to turn it off. FYI, I'm running v1.7.7 on my OC220 V1 controller.

- Do I need to disable Application Optimized Routing? Or a don't care?

- With the G4AR LAN1 connection to the LAN side of the firewall ... I have all sorts of issues with LAN traffic, and slow internet response (from other machines). If I disconnect this link, it improves. Huh? It should be set up this way, right?

- WAN2 never shoes as Online ... even when I manually enable it on the G4AR. Known issue?

- If the G4AR is disabled (not backup), ping through WAN2 still passes? Huh? It shouldn't ;).

Thanks!

  @JEJ3 A bit more on this - and not sure I fully understand how this happens :(. When I connect the G4AR LAN1 port to my LAN (as I'm supposed to do, for internet connectivity monitoring) ... my LAN DNS server changes? Huh? How can this happen? And how to avoid that of course?

Thanks!!

Sorry, @arrmo.   I can't answer your questions but I would think you need to not have your G4AR ports both connected to your router.    Connect your G4AR LAN1 port to a WAN interface on your TP-LINK router.   Do not connect anything to the LAN2 port from the G4AR.   Server up your LAN clients from the TP-Link Router.

Not familiar with your device but I needed to:

1. enable load balancing between my two WAN ports. I weighted it 100 to Comcast and 1 to T-Mobile.

2. create a Link Backup rule from the primary WAN port (comcast in my case) to the seconday WAN port (T-Mobile G5AR)

3. configure online detection for WAN Port 1 (comcast to ping 8.8.8.8 and DNS 1.1.1.1).  I left WAN port 2 (T-Mobile) as automatic

Good Luck

  @JEJ3 Thanks! But a bit confused - here's why :)

1) LAN1 is supposed to be for internet detection, right? So needing to be on the LAN side of the firewall? I am wanting to use Automatic Backup (from T-Mobile)

2) The other settings make sense, fully agree with you

Thanks again.

  @arrmo 

1) LAN1 is supposed to be for internet detection, right? So needing to be on the LAN side of the firewall? I am wanting to use Automatic Backup (from T-Mobile)

This is not a correct statement.   LAN1 and LAN2 are two ethernet connections which will each be assigned an IP address.    You are using your TP-LINK as the router and it should be assigning IP addresses to ALL computers on your network (just not your T-MOBILE or other Internet connection).    

Step 1 - Assuming your TP-LINK device has support for 2 or more WAN ports, plug your primary (in my case COMCAST) into WAN1 and LAN1 from your G4AR into the WAN2 port on your TP-LINK device.

Step 2 - Plug your other network devices (like a WIFI Access Point) into you TP-LINK routers LAN ports OR plug a SWITCH into the LAN port and then plug your devices into the SWITCH

Truthfully, you need to fire up a chat with ChatGPT or Copilot and tell it what you have and it will tell you more or less how to configure everything.

Good Luck