Multiple BAD_ADDRESS in DHCP showed up again

Tiras25
Tiras25 used Ask the Experts™
on
What is the reason for multiple BAD_ADDRESS in DHCP?  Description - This address is already in use.  I deleted them already few days back.  They came back for some reason.  About eight of them.
And it seems they show up after a an abrupt power outage we had.  Not sure if related.

Server 2016 Domain Controller.
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Distinguished Expert 2018
Commented:
The most common cause is a rogue DHCP server. Or a DHCP scope with addresses that have also been statically assigned. The DHCP server attempts to assign them to a requesting device and the result is a conflict, and thus a bad address designation.
DrDave242Principal Support Engineer

Commented:
They came back for some reason.  About eight of them.

Are those addresses all in sequence, or are they random?

Author

Commented:
Thanks Cliff.  I guess I need to find those devices.  Let me think how...

Somewhat in sequence but not really.  
.100
.105
.106
.117
.118
.120
.123
.124
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DrDave242Principal Support Engineer

Commented:
If you ping those addresses, do you get a response?

Note that a lack of a response on a given address doesn't necessarily mean that address isn't in use, as there could be a device there with a firewall that blocks ICMP traffic. If you do get a response, though, the address is unquestionably in use by something.

Author

Commented:
Yes, they are all pingable.  3 of them I can even resolve a hostname with ping -a ipdaddress
JohnBusiness Consultant (Owner)
Most Valuable Expert 2012
Expert of the Year 2018
Commented:
Get Advanced IP Scanner (Famatech - Free) and run it. It should give you information about the devices. It does for me.

Author

Commented:
I'll try thanks John!
Shaun VermaakTechnical Specialist
Awarded 2017
Distinguished Expert 2018

Commented:
Enable conflict detection with this PowerShell. Most of the times I see BAD_ADRESS it is because of static addresses in a range
Set-DhcpServerSetting -ConflictDetectionAttemps 2

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Delete the existing ones with this PowerShell
$DHCPBadReservations = Get-DhcpServerv4Scope -ComputerName $DHCPServer | Get-DhcpServerv4Lease -ComputerName $DHCPServer | Where-Object -FilterScript {$_.HostName -eq 'BAD_ADDRESS'}
$DHCPBadReservations | Remove-DhcpServerv4Reservation -ComputerName $DHCPServer

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Commented:
Is it possible some of the machines in your network have set themselves to static addresses?

If the DHCP server is not aware of those (ie, reserved IP to the MAC address of those machines) then it will give out those IP addresses not knowing that someone has use that same address manually.

You could power down all machines, and bring them up one at a time WITHOUT the DHCP server running, and see if you can ping those addresses. If you can, then they are set manually and now you know which machine is using an address incorrectly.
arp -a  on the command line should show the matching MAC addresses to help you id the system.

Commented:
Serialband, will arp show multiple systems matching MAC addresses or only the first to answer?
It will show multiple MAC using the same IP.

Commented:
Thanks. I did not think that would work as I never used it for that. I learned something new today!  :-)
You do have to be on the same subnet to get the correct arp -a results.

Commented:
That much I could figure out!  :-)
JohnBusiness Consultant (Owner)
Most Valuable Expert 2012
Expert of the Year 2018

Commented:
@Tiras25 - Thank you and I was happy to help.

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