Hi,
I’m really puzzled about an IP in our subnet that’s in use (verified via Torch, Simple Queue, etc.), but is not found among DHCP leases. I can’t locate it in our system (Ubiquiti and Mikrotik).
The IP has not been issued as a static address.
The MAC number associated with the IP indicates a Netgear router.
Under what circumstances will this occur?
Hardware is an RB433AH, approximately 220 leases issued, ver 5.12.
Thanks for any suggestions.
It could be assigned by DHCP and afterwards the DHCP server was reset.
Since the assignment never timed out, the Netgear router will retain the assigned IP and consider it valid and the DHCP server will have no clue about it and will not show it in the lease list.
With the number of power outages we have here, a reset as you suggest could well be the issue.
If this is the case, blocking this IP might force the user to reboot and obtain a lease normally.
In the past I’ve spent hours looking for a method to do this. Nothing I’ve found or my own attempts will successfully block an IP.
If you have any suggestions, I’d certainly appreciate it and many thanks for your help.
One of your options would be to shorten the lease time in the DHCP server options to, say, 15 minutes.
Then you will have this situation only a short time…
by default all the leases are restored.
In your case it looks like someone just assigned IP address to its router and that is it.
To overcome that, you can set arp=reply-only and inscruct DHCP server to add arp requests for leases it is giving out. That way everybody should be forced to use DHCP or else, networking simply will not work.
Many thanks for your input on this situation.
As far as shortening DHCP lease time, it appears this would take effect when a lease is renewed after the existing lease expires. If this is the case, I’m not sure there would be any advantage to changing the lease time.
I’ve added ARP to the lease. Again I wonder if this is the right approach since it appears this errant IP has no lease which might expire. As it is, all existing leases already list MAC information. When I test both shortened lease times and the ARP requirement, I see no difference in any data returned from the router when leases are renewed.
At any rate, I’ll leave this in effect for a few days and see if anything changes.
For all I know, I might have implemented the IP myself for some work I was doing. My aging mind doesn’t help things along. I have difficulty imagining who else might have done this (for whatever reason).
I appreciate the help.
The IP in question has become listed after adding ARP to the lease.
Now to find out who it belongs to 
Thanks.