I opened a case with Meraki, as my MS120 keeps changing the associated ip address on a mac address random.
The ip address is 18.104.22.168 with mac 0c:81:26:e4:40:c0. This is correct as it´s my default gateway to my ISP.
But over and over again different ip addresses is associated with this mac, and this is ip addresses which belongs to different websites many hops away from my MS120 switch so it is not possible at all to get the mac address for these remote devices.
Support have been very slow, answered me wrong and the last answer was:
This is due to having a layer 3 device downstream and the functionality of client detection. If you wish to discuss this further then please call our support line
Well, i rather just have a written explanation, but this seems to be very hard to get.
Of cause when i look at my firewall, i only see a couple of associated ip adresses to this mac address, which is correct. These are my ISP ip´s and are expected.
You talk about communicating with an IP address many hops away, so it is not L2 adjacent to you. The MS120 will not have a MAC address for it, nor does it need one. The MS120 is a L2 switch, and does not look at the L3 info (such as IP address).
A packet comes in one port, it looks up its forwarding table for the destination MAC (which in this case is simply the default gateway) and sends it out to another port.
The only MAC address requires for a host on a different layer 2 domain (as in this case) is the MAC address of the default gateway, and the default gateway is responsible for routing/forwarding the packet towards the next hop.