There are 3 ISPs connecting to 3 WAN ports of a multi-wan router (previously it was R470T+ v4, now R605).
The 2 remaining ports of this router act as LAN ports and are connected to 2 easy smart switches (SG1024DE v4) that are configured with MTU VLAN.
The switches provide wired connection to flats of the building, 1 LAN port per flat. I need the LAN ports to be isolated from each other but getting internet from the R605.
We needed easy smart switches configured with MTU VLAN to be prepared for any router-on-a-stick situation because in the flats people can connect their devices either directly wired or using their own wifi router which may accidentally be configured as DHCP server which would act as rogue server in an unmanaged local network.
(The uplink port on the switches is port1, but that's irrelevant.)
When I replaced the R470T+ with the new R605, first I realized that its setup page deals with VLAN configuration differently from R470T+, so I just let it on default setup without creating different VLANs for the R605's LAN ports. I think all ports are on the default VLAN1 now. But I thought it doesn't really matter because the switches must isolate their LAN ports anyway. If I created different VLANs for the router's LAN ports, the only benefit would be isolating traffic between the two switches, right?
What happened was suddenly a router (TP-Link WR740N, connected to one switch port) started to act as rogue DHCP server, trying to give IP for other devices connected to other switch ports.
Note that there are several routers in router mode (DHCP on) connected to the switches and none of them caused this issue, none of them appeared as rogue server.
It didn't matter if I connected that rogue router to a different switch port or to the other switch, it kept acting as rogue server.
I find it odd.
One detail that might matter: the rogue router has the same IP range (192.168.10.x) as one of the ISP's router connected to the first WAN port, that is a (remotely controlled by the ISP) Ubiquity device that I don't have access to modify anything in it.
Is it possible that there is a flow, a bug on R605 that causes this mysterious issue?
The R605's LAN is set to a different IP range (192.168.6.x).
Do I have to setup the LAN ports on R605 with VLANs different from the default VLAN1 to avoid this issue? And if so, what would be that setup (in standalone mode)?
There are only instructions for router connected to L3 switches, creating different IP pools etc... that is not our case.