RT-AC86U - Dual WAN setup question...

BosseSwede

Regular Contributor
I have installed an RT-AC86U running stock firmware 3.0.0.4.386_48260, which I believe is the latest f/w. It is the router for a new fiber connection on my summer cottage.
Now I also want to correctly enable a Dual-WAN configuration where if the fiber fails a 4G Mobile Broadband modem kicks in as the connection.
I have checked this when I was initially working on the router at my home and it seems to work to connect to 4G and use this as the WAN when the main wired WAN is not present.

The router is now installed minus the 4G mobile modem but I am going out there on Tuesday and want to get it correctly set up then.

So this is the way it looks now:

1653247833611.png


What I am worried about is the [ ] Allow fallback checkbox...
If it is unchecked will that mean that if a failover happens due to fiber outage and the 4G modem kicks in then the router will stay on 4G indefinitely without going back if fiber connectivity returns? This can absolutely NOT be allowed to happen!

Also, the last two checkboxes (DNS query and Ping) need some consideration, what do they mean? And how should they be set? If left unchecked will the fail-over/fail-back never happen?

Since fiber has unlimited data whereas 4G has a monthly allotment (not much data) I want to use 4G only if the fiber is down.
And I need to detect that the fiber is down on a couple of client Linux boxes so they can stop performing data intensive tasks when this happens and the secondary WAN is active.

Can the state of the router connection be checked from a client device somehow?
Maybe by detecting the external IP address of the system or similar?
Can someone here suggest a bash script command which will do this detection?

Thanks for any advice!
 

Tech9

Part of the Furniture
Dual WAN failover and failback is very unreliable in Asuswrt. You have to experiment what works for you. Don't be surprised to find your 4G plan completely drained because the router did not failback. Read this thread and see if the script will help in your case:


You'll need Asuswrt-Merlin firmware to run the script. Won't work in stock Asuswrt.
 

BosseSwede

Regular Contributor
Oh boy!
I don't want to go down that rabbit hole...
Will refrain from using WAN fail-over then (will not plug in the 4G modem).
Thanks for the warning!
 

Tech9

Part of the Furniture
Multiple threads here on SNB Forums about Dual WAN issues. No good solution found so far and it was never fixed by Asus. The custom script gives a new hope, but requires custom firmware too. Dual WAN is one of Asuswrt features for advertising purposes only, unfortunately.
 

jrusling

New Around Here
Multiple threads here on SNB Forums about Dual WAN issues. No good solution found so far and it was never fixed by Asus. The custom script gives a new hope, but requires custom firmware too. Dual WAN is one of Asuswrt features for advertising purposes only, unfortunately.
It has been my experience that if you have dual WAN enabled, the OpenVPN server will never complete starting up.
 

BosseSwede

Regular Contributor
How about the OpenVPN client?
I am using this to connect my remote LAN to my home LAN, but I have a dedicated Ubuntu Server as the OpenVPN server on the home LAN so not relying on the router's OpenVPN server function.
 

Ranger802004

Senior Member
Dual WAN failover and failback is very unreliable in Asuswrt. You have to experiment what works for you. Don't be surprised to find your 4G plan completely drained because the router did not failback. Read this thread and see if the script will help in your case:


You'll need Asuswrt-Merlin firmware to run the script. Won't work in stock Asuswrt.
Thanks for the reference to my script. Yes the script makes Dual WAN failover and failback very reliable, I've had a lot of good feedback and suggestions and have made several patches to the script to add features and resolve issues outside of what I'm able to test in my environment.
 

BosseSwede

Regular Contributor
The router is now installed minus the 4G mobile modem but I am going out there on Tuesday and want to get it correctly set up then.
So I was out this week and the first day the ISP had warned about maintenance on the fiber would affect my connectivity.
So I plugged in my USB 4G modem and waited for the outage.
When it happened there was no failover, the LAN was disconnected even though the modem itself signalled its connected state!
The RT-AC86U did not connect the modem even though the WAN provided no Internet connectivity!
I had to unplug the WAN network cable for it to instead use the 4G modem!

Later when the maintenance outage was over I reconnected the WAN cable and the router still stayed on the 4G!!!
I had to power cycle the router in order for it to use the fiber WAN.

So the verdict is that 4G failover does not work, the router itself can handle the 4G WAN but only with manual interaction, so no auto switching in either direction...
 

Smokey613

Very Senior Member

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