Hi, I hope to post in the right place.
I have three nets (192.168.81.xxx, 192.168.82.xxx, 192.168.83.xxx) and I have to connect, for maintenance, directly in these nets.

E.g., I have a device with IP address 192.168.82.7 and I can access it through a router.
Sometimes the device resets and takes the factory default IP address (1.2.3.4).
I can't reach it from my PC, so I have to connect directly on 192.168.82 net and run its own program to change the IP.

I would like to use a RB133 with three ethernet ports to leave me connect directly to every net.

Eth1 = 192.168.81.xxx
Eth2 = 192.168.82.xxx
Eth3 = 192.168.83.xxx

I connect my PC through Wlan1 (I have 192.168.81.xxx address) when I need to connect to this net, then I change my PC IP to 192.168.82.xxx and I still connect to 192.168.82.xxx net.
Is it possible make this?

Thanks.

Say you set up your 133 router with three interfaces:

ether1 : 192.168.81.1/24 -> connected to a switch will all of the 81.x devices
ether2 : 192.168.82.1/24 -> connected to a switch will all of the 82.x devices
ether3 : 192.168.83.1/24 -> connected to a switch will all of the 83.x devices

On all of your devices on the 81.x network, set the default gateway to be 192.168.81.1.
On all of your devices on the 82.x network, set the default gateway to be 192.168.82.1.
On all of your devices on the 83.x network, set the default gateway to be 192.168.83.1.

Then all devices on all networks will be able to see all devices on all networks. Your laptop will be able to see all devices on all networks too.

BUT if your suspect device that keeps reverting back to 1.2.3.4 or whatever, then you will have to set up the laptop in the same network as this (81.x, 82.x or 83.x) and when it does this, just give your laptop 1.2.3.5 and you will be able to reach it.

The gateway (192.168.xxx.1) is already present in the network, I can't assign to the ethernet port the IP address of the gateway.