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DHCP Bad_address

We just setup a new DHCP scope and we are getting some bad_address's that are coming up in our console. Im checking but I do not find any other device other than our DHCP server that is handing out ip addresses. What else can I do to troubleshoot this? I look at the logs and everything looks okay.
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Thomas N
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Thomas N
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Thomas NSystems Analyst - Windows System AdministratorAuthor Commented:
What if I reserve those "bad_address" ips, will this force the machine to use a different ip? We have plenty of ips in that scope.
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PberSolutions ArchitectCommented:
It might just be static IP already within the scope.  If an IP is marked Bad, dhcp will no longer attempt to use it.  Try and connect to those IP addresses via RDP or remote management tools to find out if they are Windows devices and check the TCP/IP settings
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Thomas NSystems Analyst - Windows System AdministratorAuthor Commented:
i did lower the lease time to 3 hours because we recreated the scope and wanted to make sure addresses were being renewed
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Cliff GaliherCommented:
It is almost always an IP address conflict. Either from static, or another DHCP server or otherm
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Richard FrankSystems AdministratorCommented:
I had the same issue a while ago, A device on the network that acted like it took all those IP numbers.

this problem continued untill the pool was full and DHCP couldn't assign IP addresses,
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Thomas NSystems Analyst - Windows System AdministratorAuthor Commented:
Richard,
  so what happened after the pool was full? How did the problem go away. Thanks
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PberSolutions ArchitectCommented:
Yeah, if you recreate the scope that would happen.  When did you lower the lease time, Prior to recreating?  How long was the previous lease time.   It should clear up when all the clients renew on the new scope.
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PberSolutions ArchitectCommented:
Looking back at your original question.  This is likely expected behavior since you recreated the scope.  

Existing clients will retain their existing IP until they attempt to renew their lease (First renew attempt is at 50% of lease time).   So if you had a lease time of 4 days, then at 2 days it would attempt to renew.  If you lowered it to 3 hours, it would only pick up that change at the first renewal attempt of 2 days.  

Since you re-created the scope, the MAC to IP mapping that the DHCP scope uses is gone.  So DHCP server will attempt to hand out IPs at the start of the scope to new clients and clients renewing.   DHCP conflict detection (likely turned on) will attempt to ping the IP before handing it out to ensure it is free.  Since you already have existing clients using those IP from the previous DHCP scope, the DHCP server marks it BAD and attempts the next IP address until it can find a free one to hand out.

I expect this is your issue.  If you have lots of lease space free, you it should clear up when all the clients renew based on their old lease.
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Thomas NSystems Analyst - Windows System AdministratorAuthor Commented:
Thank you
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PberSolutions ArchitectCommented:
no problem
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