Two OpenWrt, Two WAN, how to setup - also Wman3

Hello everybody,
I need your expertise to help me to solve a particular case:

As it is now:

primary router:

  • OpenWRT 19.07.1 on linksys WRT1200AC
  • LAN: static ip address:
  • WAN: ADSL modem plugged in the WAN port
  • WANB: 4G iPhone 5s plugged in the usb as backup line
  • Mwan3 as load balancing, configured with WAN primary, WANB backup line
    (used this procedure
  • a trick to route back the VPN connection from WANB to WAN after primary DSL line recover, if not the VPN connection remains on backup line (here: Mwan3 not reverting back to main wan)
  • SQM QoS in both WAN WANB to ensure the best performance against buffer bloat

cascade router:

  • OpenWRT 19.07.1 on linksys WRT1900AC
  • LAN: static ip address:
  • LAN: gateway: the primary router, so

What I want to do:
the 4G modem signal is just fine on the place where is installed the primary router,
, so I am wonder if I can move the 4G router in the secondary router, and I am in trouble
about the WAN / WANB settings in the secondary router.

primary router:
WAN: the physical WAN port to the DSL
WANB: the secondary router, so
Mwan3 will route the traffic properly using WAN as primary, and WANB as backup

secondary router:
somehow a WAN the route to the primary router
WANB: the 4G iphone 5s as backup line
Mwan3 will route the traffic properly using WAN as primary, and WANB as backup

My difficulty is that I should create a interface WANB on primary router, WAN on secondary router
that uses the LAN interface, I am worried to mess all up.

thank you

This is not exactly cascading. You have 2 routers in the same network. So you are advertising the IP of the primary router as the gateway to the lan hosts.
If you want to move the 4G to the secondary router, it would make more sense to create a dedicated link between the 2 routers and thus avoid having any issues from routing asymmetries.

ciao Trendy,
thank you for your reply, actually right now I have a dedicate link between the two router linksys,
I am using a ethernet cable that connect them from switch-lan to switch-lan.

are you suggesting that I can somehow connect them both? can you indicate the way to follow?

thank you in advance

I suggest that the port which you are using to connect the 2 routers on the main router should be a dedicated wan port, not part of the lan.
For example 1200AC will have and 1900AC
Then you will use this new interface in mwan3 for your load balancing and failover.