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Unknown device in ARP list with IP and without MAC

Posted: Tue Apr 30, 2019 10:39 am
by mpixel
I have unknown device in ARP list.
With IP address but without MAC address.
Only Flag "dynamic"

How do I find out what this device is ?

I thought every device must have a mac address.

Re: Unknown device in ARP list with IP and without MAC

Posted: Tue Apr 30, 2019 11:11 am
by Jotne
Does it show up in your DHCP-server?
/ip dhcp-server lease print

Re: Unknown device in ARP list with IP and without MAC

Posted: Tue Apr 30, 2019 12:58 pm
by mpixel
I can´t see it in DHCP Leases.


You can see in attached pictures.
IP 10.10.110.31

Re: Unknown device in ARP list with IP and without MAC

Posted: Tue Apr 30, 2019 1:17 pm
by Exiver
That happens when your router tries to reach that address but no device is answering (ARP)

You can easily try this out:

* Check /ip arp
* Try to ping an address which is not in use
* Check /ip arp again

Re: Unknown device in ARP list with IP and without MAC

Posted: Tue Apr 30, 2019 6:11 pm
by mpixel
Why does my router try to reach that address?

I don´t have such ip address in DHCP.

ping 10.10.110.31
timeout

Re: Unknown device in ARP list with IP and without MAC

Posted: Tue Apr 30, 2019 6:24 pm
by Exiver
It doesnt mean that only your router tried to reach that address. Could be some device in another subnet for example. The timeout is expected since that device is not reachable. It was just to show you that the entry appears in dhcp-server leases with only "D"-Flag and without mac-address...

Re: Unknown device in ARP list with IP and without MAC

Posted: Tue Apr 30, 2019 6:37 pm
by mpixel
But how do I know which device is it in our network when I don't even know its MAC address?

Re: Unknown device in ARP list with IP and without MAC

Posted: Thu May 02, 2019 2:35 am
by Exiver
The device is not in your network... Some other device has tested whether this ip is active or not. It seems to be not active. If you want to know which device asked for that ip you need to log arp messages on your L2 network and search them when somthing similar happens again..

Re: Unknown device in ARP list with IP and without MAC

Posted: Fri May 03, 2019 3:25 pm
by mpixel
It happens continuously. Apparently some device is looped.

Will you advise me how to do this?
I don't know what to log. I want to know MAC address of this device -then I will be able to find a vendor and thereby reduce the list of possible devices narrowed down, for example, to printers or mobile phones