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Bad IP Address in my DHCP

Discussion in 'Networking' started by Pmdown, Oct 1, 2019.

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  1. Pmdown

    Pmdown Thread Starter

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    Hi Guys am Administering around 200 Computers and around 30 Digital Medical Machines , ihave a challenge with BAD IP ADDRESS in my DHCP , it has reached the extent of disconnecting Internet access to clients /Staff , i have tried to eliminate the Wireless Access Points one by one but i still get BAD IP ADDRESS, is there any one with a quick solution?
     
  2. zx10guy

    zx10guy Trusted Advisor Spam Fighter

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    What do you mean by bad IP address? Are you referring to the DHCP server handing out addresses which another client device has already been assigned?
     
  3. Couriant

    Couriant Trusted Advisor

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    It sounds like that you have devices that have IPs possibly assigned statically somewhere. Can you ping the devices / find them in ARP?
     
  4. Pmdown

    Pmdown Thread Starter

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    Yes BAD Address under Adress Leases which assigned to clients Automatically by DHCP
     
  5. SeanLaurence

    SeanLaurence

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    This is not an easy problem to fix.....
    Start with a program like NMAP (opensource) or Angry IP Scanner (Windows Freeware) to map out your subnet.
    Either program attempts to identify the equipment at each IP address, with varying results.
    Use the results to compare with your DHCP server's list to account for all your known systems and IP addresses.
    I understand that some systems can be set up to not allow unknown systems to work on your network.
    You might have somebody who plugged a device into a live network port and set it up with a fixed IP address that they guessed at. If they split a line with their own switch, then you would have a hard time detecting it.
    Are you working with managed switches? If you are, then what make and model? This would help someone guide you through any further lockdown steps
     
  6. SeanLaurence

    SeanLaurence

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    What DHCP server are you running? Windows Server ? Linux Server? The DHCP on your router? What version or Make and model?
    Are you able to spot any trends? Is it the same IP address(s) that is/are consistently a problem? Are you able to identify one or both of the pieces of equipment involved with the conflict.
     
  7. Pmdown

    Pmdown Thread Starter

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    @ Couriant i have so many devices so which one should i start with?
     
  8. Pmdown

    Pmdown Thread Starter

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    Yes Sean , thanks so much for the guide , am gong to try that , meanwhile am running Windows Server DHCP and am not using managed Switches, am challenged that am Running two buildings with out the VLans
     
  9. SeanLaurence

    SeanLaurence

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    You didn't specify which version of MS Server you are running....
    You might want to try turning on "IP Address Conflict Detection"
    https://docs.microsoft.com/en-us/pr...ows-server-2008-R2-and-2008/dd183587(v=ws.10)

    Is your facility operating 24/7? Would you have an opportunity to disconnect the Server running DHCP from the network for a test to see if there is another rogue DHCP server operating on the network (Plug in a device and see if it is given an IP address)
     
  10. Pmdown

    Pmdown Thread Starter

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    Sean am Running 4 servers , but my DHCP Server is running on Windows Server 2018 R2 Enterprise mean while i have installed the NMAP seem so helpful, though its abit late here i have to break off until tomorrow morning , i really appreciate Sean , will get back to you tomorrow
     
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