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IP conflicts after converting to DHCP reservations

    Question

  • I have an odd issue on some hosts (Windows XP and 7 and iOS X) after converting to DHCP reservations:  I get an IP conflict message even though I know that there is no other device on the network using the machine's reserved IP addresses.  The only way to resolve the issue is to delete the reservation and let the DCHP server dish out an address of its choosing.

    If anyone knows what could be causing this issue (apart from an actual host on the network using the reserved IP address) I would be grateful to hear about it. As I said above, I am certain there's no other machine on the network using the reserved IP address.

    Thanks,

    Steve

    • Moved by Santosh BhandarkarMVP Friday, April 26, 2013 2:42 AM Moved from Server General forum to more appropriate one
    Thursday, April 25, 2013 6:55 PM

All replies

  • Is it a reservation or an exclusion?  

    Try ipconfig /release and ipconfig /renew and see if the issue is still there. 

    Regards.

    RW

    Thursday, April 25, 2013 9:36 PM
  • Thanks for your reply.  It's a reservation.  If I renew the lease I get the same IP and the conflict is still there.  It's a /23 network, and the thought hit me that maybe there's a host(s) with the wrong subnet mask that is only looking at the last octet for the host address so that 192.168.0.59 and 192.168.1.59 look like they're conflicting.  In that case, though, would 192.168.1.59 even see 192.168.0.59 because they'd be on different networks from one another if they had subnet mask 255.255.255.0?

    I appreciate your suggestions.

    Steve

    Friday, April 26, 2013 12:49 PM
  • Hi,

    Thank you for the post.

    Please check if there is a client configured as the static one in the network, so when the problematic client get the same IP address from DHCP, it will report the conflict mark.

    Regards,


    Nick Gu - MSFT

    Monday, April 29, 2013 2:17 AM
    Moderator
  • Thanks for your reply.  I can't find a clients withe static IP addresses matching the ones for which I'm getting the conflict notices.  In one case restarting the affected client machine seems to have resolved the issue (unless it's coincidental).  I'll keep trying to find a machine with a manually applied IP address.

    Steve

    Monday, April 29, 2013 2:42 PM
  • Ping both IPs, then run arp -a to get their MACs. Then look the MACs up in your switch, find the port, trace it to the patch panel.

    If you have a reverse zone, try to also ping it with ping -a 192.168.x.x to see what name it's associated with, but this isn't usually accurate, especially if the reverse has duplicate or incorrect entries.


    Ace Fekay
    MVP, MCT, MCITP/EA, MCTS Windows 2008/R2 & Exchange 2007, Exchange 2010 EA, MCSE & MCSA 2003/2000, MCSA Messaging 2003
    Microsoft Certified Trainer
    Microsoft MVP - Directory Services
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    This post is provided AS-IS with no warranties or guarantees and confers no rights.

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    Monday, April 29, 2013 4:09 PM