MS120 arp table

Getting noticed

MS120 arp table



I opened a case with Meraki, as my MS120 keeps changing the associated ip address on a mac address random.

The ip address is 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.


The switch is running 14.28. 


A drawing of the network can be seen here


Can anyone explain this MS switch arp behavior?






Kind of a big deal
Kind of a big deal

I dont know the ms120 but isnt it just layer2?

It does not have a arp table?


I think you hairpin packets on the ms and that messes up reporting. I supose it would be better to connect isp router to the firewall if you would like that corrected

Getting noticed

You are wrong, the cause the MS120 has a arp table. Does every L2 device not have this when talking ethernet, hmm.


Anyway, i do not know what you mean by "hairpin packets".


I do not understand the issue.


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.

You are right, sorry, farwarding table what i ment to say.


I agree with you. But then i do not understand how Meraki dashboard shows the client list. here is from my vlan98:


# Description Usage MAC address IP address Adaptive Policy Group VLAN Port

1 0c:81:26:e4:40:c0 14.67 GB 0c:81:26:e4:40:c0 98 1
2 5c:76:95:98:f7:ec 1 KB 5c:76:95:98:f7:ec 98 1
3 00:01:21:2a:cb:78 15.44 GB 00:01:21:2a:cb:78 98 7
4 02:10:18:98:f7:f0 1 KB 02:10:18:98:f7:f0 98 1


Number 1 is not in my broadcast domain.

Number 2 i believe is my cable modem

Number 3 is my ISP gateway

Number 4 i have no clue


Why do i see number 1 entry? 

Kind of a big deal

Your firewall doesn’t happen to be a Juniper does it? 0c:81:26:e4:40:c0 is a Juniper MAC address.

No, i have a watxhguard.



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