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rogue dhcp server or bad reservation? our conflict detective work

Solveddhcpip-conflictlan11 replies · 434 views · started
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Accepted solution by Xavi M. — The most common cause is a static IP confiugred inside the DHCP pool. DHCP doesn't know it's taken and hands it out again. Either move…
  1. Rowan Lund
    @copper_rider-112

    not gonna lie this is driving me nuts users report random no network issues and some PCs pop up an IP conflict warning:

    Network & internet

    Network & internet
Wi-Fi  •  HomeNet_5G
No internet, secured

Connected, but nothing loads. Troubleshoot problems?

    our scope is 192.168.0.0/24. i set a security caemra to a static address years ago and honestly dont remember which one. could that be related?

    i supsect our IP plan, if you can call it that, has some issues. A few devices were configured by hand years ago and nobody documented anything. How do i safely untangle this without breaking things?? any ideas??

    rage

    5
  2. Gabe O.
    @gabe.ortiz8

    hmmm do u have managed switches where you can look up MAC addresses? ??

    2 0 helpful
  5. Gabe O.
    @gabe.ortiz8

    oh ive been there lol prevent rogue servers with DHCP snooping on managed siwtches: mark the uplink to your real DHCP server as trusted, all other ports untrusted.

    29 0 helpful
  8. Kofi
    @kofi_tiny

    If clients get addresses outside your scope, you have a second DHCP server: often a consumer router someone plugged in, or a device with DHCP enabled by default. On Windows, ipconfig /all shows teh DHCP Server address teh client actually used. Then find and unplug it.

    1 0 helpful
  10. Eamon
    @emoreau_35

    oh ive been there lol on a Windows DHCP server, enable conflict detection (IPv4 server properties, Advanced tab, Conflict detection attempts set to 1 or 2). the server pings an address before leasing it 😤 it slows leasing slightly but prevents duplicates from static devices.

    24 0 helpful
  11. Xavi M.
    @xavi_pixel
    Accepted solution

    The most common cause is a static IP confiugred inside the DHCP pool. DHCP doesn't know it's taken and hands it out again. Either move static devices outside the pool or create DHCP reservations for them instead of static configs.

    4 5 helpful

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