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    speckytecky's Avatar
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    Server 2008 DHCP conflict issue

    One of my schools has a MS 2008 Standard Edition domain and mostly XP Pro Workstations. The domain has been running pretty stable for about a year now. Recently though there have been a few DHCP Conflicts. I have tried Ipconfig / flush and renew but notice the same IP address gets allocated. ***.***.**.204 and . ***.***.**.205

    Nothing seems to be actually sharing these IP addresses but from the old Server 2003 domain (it had a different name from the current one) I have a vague recollection that the scope then went up to 200 and 204 and 205 had been assigned outside the scope to wireless kit thatís no longer in school. The scope was extended about a year ago and now goes up to 250.

    Would I be right in thinking that I can delete 204 and 205 from the current register. Run flush and renew from the computers again and hopefully they will pick up new IP addresses or do I need to set something to block 204 and 205

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    Killer_Bot's Avatar
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    So can you ping 204 & 205 when the computers you're talking about aren't online? If you can then you need to find where those IPs are or maybe just exclude them if you can't be bothered. Deleting them from the database wouldn't help until they come to renew the IP with the DHCP server and get refused, and depending on your lease time you could be waiting a couple hours or weeks.

    There is another option on the DHCP server where you can configure conflict detection so that it attempts to ping an IP before issueing it to a client. Maybe configure that and if it gets a response on 204 it'll try 205 to which again it'll get a response and got to 206. Depends how you want to go about it.

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    speckytecky (12th February 2011)

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    Thanks Killer_Bot for your answer.

    I ran a report on Spiceworks and can see where my conflict is arising now.

    The folk who upgraded the switches put in managed switches and allocated them IP addresses which were at the time outside the scope.

    Since we extended the scope they are now included and from the Spiceworks report I can now see them - allocated to the switches and in the new extended scope also picked up by DHCP and allocated to PCs.

    What would be my best way round sorting it out - setting the IP addresses for the switches as Reservations perhaps then the computers will pick up fresh IP addresses next time they log on?

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    You could do reservations for the switches though you'd want to configure the switches to DHCP then (to pick up the reservation) though I imagine leaving them as static would be fine. Plus setting anything that requires a Static IP as a DHCP reservation can end badly should the DHCP go down whereas statics would obviously survive.

    If I were you though I'd just set up a new exclusion range for ***.***.***.204 - ***.***.***.205 (e.g 192.168.1.204 - 192.168.1.205). Those IPs would never get dished out then.

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    speckytecky (14th February 2011)

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    If possible i would place your switches (then management interface that is) in a seperate VLAN for security reasons.

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