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We are using a private 10.0.0.0/8 network for the management and other local traffic (storage) in our LAN as shown in the symbolic layout here:

10.0.0.1                  10.0.0.2
Gateway                   Linux Device
   ^                           ^
   |                           |
   |                           |
   v                           v
Layer-3-Switch-A <----> Layer-3-Switch-B
       ^
       |
       |
       v
    10.0.0.3
    Linux Device

My question is, how one can track the 'real' flow between the local Linux devices on the switches and gateway. Especially if a packet is flowing thru the 10.0.0.1 gateway, even if the source is 10.0.0.2 and the target is 10.0.0.3 in the given layout. I know there are different capabilities of switches that should be able to tag the packets to be not routed thru the gateway each time, but as I have not all specs and knowledge about each switch and the gateway, I wonder if there are some tools to trace this (like tcpdump and alike).

Our main fear is that each package is going thru the gateway, before it is travelling back to its target because of e.g. wrong capabilites of the switches or simply wrong settings.

Any help is welcome!

3

I know there are different capabilities of switches that should be able to tag the packets to be not routed thru the gateway

That's not how switches work. They forward frames based on the MAC address of the frame. One way to check is to look at the MAC address table of both switches. You should be able to see the MAC addresses of your hosts associated with the correct ports. That's what the switch uses to determine where to forward packets.

Our main fear is that each package is going thru the gateway, before it is travelling back to its target because of e.g. wrong capabilites of the switches or simply wrong settings.

You would have to significantly (i.e., deliberately) misconfigure your switches to make that happen, and probably other things would break as well. As long as your hosts have the correct address and subnet mask, you can be confident that traffic between the Linux devices is not going to the gateway.

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