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MONDAY 8AM: THE CONFERENCE ROOM TV OFFLINE, AND THE CULPRIT IS A DUPLICATE ADDRESS !!

dhcpip-conflictlan16 replies · 235 views · started
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  1. Kira
    @kiras437

    ugh. 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 10.10.20.0/24. i set the conference room TV to a static address years ago and honestly don't remember which one. could that be related?

    I suspect 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?

    13
  2. Maya S.
    @maya_shader

    Is mini PC configured with a static IP, and is that address inside the DHCP pool?

    2 0 helpful
  3. Kira
    @kiras437
    in reply to @maya_shader

    ok so the conference room TV has a static IP right in teh middle of the DHCP range of 10.10.20.0/24... yikes.

    5 2 helpful
  4. Xavi Yilmaz
    @xavi.yilmaz8

    ok so my gaming rig is officially haunted thx in advance!!

    1 5 helpful
  5. Bo Dalton
    @cipherprobe

    lol same thing happened to me if clients get addresses outside 172.16.10.0/24, u have a secnod 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 the client actually used 😂 Then find and unplug it.

    0 2 helpful
  6. Esme C.
    @esmec862
    in reply to @cipherprobe

    ok update: did what @xavi.yilmaz8 said and its fine now 🤦 this. so much this cant believe it was that simple lol

    party

    2 0 helpful
  7. Xavi Yilmaz
    @xavi.yilmaz8

    ok so prevent rogue servers with DHCP snooping on managed switches: mark teh ulpink to ur real DHCP server as trusted, all other ports untrusted. hope that helps :)

    2 0 helpful
  8. Leon R.
    @leon.rossi12

    oh ive been there lol the most common cause is a static IP configured 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. worked for me anyway 🤷

    20 0 helpful
  9. Caleb Costa
    @tinyowl

    been there man honestly just reset teh cable and save yourself the pain fingers crossed 🤞

    1 0 helpful
  10. Kai Gill
    @kgill_10

    hmmm wait does this also apply to ip-conflict?. bump. still happening with ip-conflict for me ??

    thinking

    31 0 helpful
  12. Cyrus Ortiz
    @cortiz_35

    find who owns the IP. from a machine on the same subnet: arp -a (Windows) or ip neigh (Linux) shows the MAC for the address after you ping it. look up the MAC vendor prefix and check the siwtchs MAC address table to find teh port. hope that helps :)

    0 5 helpful
  13. Fenna
    @fenna_buffer

    ok weird one reading this at 2am instead of sleeping, no regrets

    2 0 helpful
  14. Caleb Costa
    @tinyowl

    respectfully disagree, i tried that and it made dhcp worse

    30 1 helpful
  16. Jade Iqbal
    @jade_copper

    On a Windows DHCP server, enable conflict detection (scope properties, Advanced, 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. lmk how it goes

    4 0 helpful
  17. Jade Iqbal
    @jade_copper

    been there man keep a simple IP plan: a documented range for static devices, the DHCP pool, and reservations for printers, NAS and phones 👍 It sounds boring but it ends these weekly mysteries.

    9 0 helpful

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