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Issue with different computers getting the same IP handed to them from DHCP

vmich
vmich asked
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Last Modified: 2019-01-10
We are running 2 DCs which are 2008 R2. I know we will be replacing them in the next month or so.. lol
But for now we are seeing an issue with DHCP in that there are different computers that are getting the same IP address handed to them for some reason. Nothing has really changed in the DHCP setup that has been in place for sometime now.
We are seeing this more and more frequent for some reason.
Is there something that I need to check with dhcp to stop this from occurring?
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DrDave242Principal Support Engineer
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Commented:
Do you have more than one DHCP server on the network? If not, are you absolutely sure that all of the affected machines are being given these addresses by DHCP rather than a static assignment?
nociSoftware Engineer
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Commented:
When deploying DHCP there should only be ONE DHCP server, or if there are multiple servers they need to share their leases and reservations or not have overlapping ranges to prevent mishaps.  
You may be able to split the address range in two parts and have each DHCP server only serve half of the addresses.
There there never is a colision.

Author

Commented:
There is only one dhcp server.
nociSoftware Engineer
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Commented:
A single DHCP server should not issue addresses multiple times.
Is this a case where on address from the range was configured as static address on some system in stead of making it a reservation?
It can be static, but then it should still become a reservation so no other system might get that address.
DrDave242Principal Support Engineer
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Commented:
If the affected systems run Windows, running ipconfig /all on those systems will show things like whether the assigned addresses are static or from DHCP, what DHCP server was used, and the lease time and expiration. Feel free to post that output here, if you'd like.

Author

Commented:
Ok sorry I have an update.. I listed the information wrong somewhat..
The issue is that there are duplicate IPs being handed out and weonly have one dhcp server. We hada computer that received an IP yesterday and then we put a new computer on today and it got the same IP from dhcp as the computer yesterday had and so we got an IP conflict..
This is very strange and I am wondering if maybe this could be related to a dns issue or would it be all dhcp?
Scott SilvaNetwork Administrator
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Commented:
What does the DHCP logs say on the server?
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nociSoftware Engineer
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Commented:
There is a not very likely possibility that both systems have the same MAC address.
(or a network card with defective identity roms /  VM-image copied & started from another).
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Commented:
@vmich,

Were both of these machines provisioned from the same image?

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