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Clients no longer able to receive IP addresses from the primary DHCP server

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Last Modified: 2018-08-09
What would cause a DHCP server to stop handing out IP addresses to a subnet?  We have a single DHCP server that handles two different subnets - 1 & 2, that are on different VLANS on our network.  After working for several months, clients that originally have an IP leased from "subnet 1", began having trouble getting an IP assigned automatically from "subnet 2" - they just sit dormant, retaining the bad IP from the other "subnet 1".   To our knowledge, nothing has changed on the network - although something MUST have changed, somehow.  Again - this had been working fine for some time...and then stopped.  Any suggestions is much appreciated.

Update: I checked the DHCP server log, and I can see it is handing out IP's for subnet 1 to client requests coming from subnet 2.  This is the problem, but I do not know why its doing this.
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System Engineer
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Damian GardnerIT Admin

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thanks or your help.;  I checked event viewer, but nothing in there.  the DHCP log however shows requests are being answered incorrectly - subnet 1 IP's are being handed out to clients who move from the "subnet 1" area  over to "subnet 2" area of the network (another building).  since requests are making it through, it confirms its not an IP helper issue.  also have rebooted the DHCP server a couple times.
Damian GardnerIT Admin

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Could it somehow be related to the existing lease for this test machine I'm using - there is a lease on "subnet 1" that exists.  this is the IP that the server keeps giving the machine, even when its on subnet 2.  Could the lease somehow be "locking the machine in"??
MaheshArchitect
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Damian GardnerIT Admin

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I'm engaging Microsoft on this.  will let you know what the problem was.
DrDave242Principal Support Engineer
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Damian GardnerIT Admin

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Dr Dave - thanks for your replay.  Assuming that this IS what's happening, how do I counteract that?  Also - its interesting that this process of clients walking back and forth between buildings here (different VLANs), has been working ok for atleast a few months (since November) when we installed the new leg of the network.  It just suddenly stopped working.
DrDave242Principal Support Engineer
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Assuming that this IS what's happening, how do I counteract that?
That is a good question. I'm afraid I don't have an answer off the top of my head, but I'll see if I can come up with something. No changes were made to the network infrastructure around the time the issue started?
Damian GardnerIT Admin

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thanks for your help guys.  problem turned out to be due to the scopes being included in a superscope.  we don't know how that happened.  thanks again

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