How to use two multiple gateways in one subnet?

[olodar]

Hi,
I want to setup reserve router with mwan3, both gateways in single network. For example, this (reserve) router will have address 172.25.25.120/16, and two routers which it will use - 172.25.25.121/16 and 172.25.25.122/16. In virtual machine I just can add multiple bridge adapters and assign address for each wan interface (172.25.25.123/16 and 172.25.25.124/16), but how to do multiple interfaces on single port on real router?
I also tried make VLANs, but it is not working.
VLAN config:

Interfaces:

[iplaywithtoys]

It's not surprising that routing isn't working, with those subnet masks.

Your LAN, WAN1 and WAN2 addresses are all in the same subnet from the perspective of the routing table: 172.25.0.0/16

[olodar]

And? They can't use gateway in same network?

[dl12345]

Your machine has no idea whether to route the packet to the LAN, WAN1 or WAN2.

You're telling it that all three are valid routes. You need to subnet properly.

[dl12345]

can you draw a diagram of your network with the routers and the gateways and their ip addresses?

[iplaywithtoys]

If you don't have Visio or similar, I can recommend draw.io from experience (see my profile.)

[olodar]

Found workaround by using wireguard on both 'main' routers