Finding VMs with Duplicate MAC Addresses

At one of my customers' sites today, I saw an error message that I've not seen before: VM MAC Conflict.  "Well, that's certainly not good," I thought, as I poked around at the error message.  To my chagrin, I could only find that error message for a single VM in the environment, and that error message wouldn't tell me with which other VM it was conflicting.  So, I could only think of one way to figure out what was going on with this conflict: look at the MAC Address assigned to every NIC on every VM in the environment, and figure out what was causing the conflict.  Easy!

No, really, it was easy.  Had I done it by hand, I would certainly have driven myself crazy, but PowerCLI made it nice and easy.  I just used this command:

(get-vm | get-networkadapter | ? {$_.MacAddress -eq "<offending MAC Address>").parent

Lo-and-behold, it returned 2 VMs.  One was the known VM that had flagged the error and the other was a powered-off VM.  Maybe that's why it wasn't also flagging the error, but regardless, we easily identified the source of the problem and were able to resolve it.

P.S. if you ever need to find all duplicate MAC addresses in an environment, you can use these commands:

$allNICs = get-vm | get-networkAdapter
$dupeMACs = (compare-object $allNICs.macAddress ($allNICs.macAddress | select -unique)).inputObject

foreach ($thisMAC in $dupeMACs){
   "="*17 + "`n$thisMAC`n" + "="*17
   ($allNICs | ? {$_.macAddress -eq $thisMAC}).parent.name
}

Comments

  1. tabSeptember 9, 2021 at 4:49 AM

    Thank you Jason. it is really helpful for me.

    ReplyDelete
  2. UnknownApril 13, 2022 at 6:51 AM

    Jason,
    is there any powercli command to find duplicate IPs for vm's or edges in vcenter.

    thanks

    ReplyDelete
    Replies
    1. Jason ColemanApril 13, 2022 at 8:42 AM

      I would do something this:
      $allVMs = get-vm
      $conflicts = $allVMs.guest.ipaddress | group-object | ? {$_.count -gt 1}
      foreach ($ip in $conflicts.name){
      echo $ip
      $allVMs | ? {$_.guest.ipaddress -contains $ip}
      }

      If you want to get fancy, you could create an object with IP Address and VM properties, and then record the address and list of VMs into their respective properties, then return that object into an array and convert the array into a csv... or you can just scroll down your window and look at which systems are using which address.

      Delete
    2. sdineshgandhiJune 11, 2023 at 11:15 PM

      Thank you Jason..

      Delete

Post a Comment

Sorry guys, I've been getting a lot of spam recently, so I've had to turn on comment moderation. I'll do my best to moderate them swiftly after they're submitted,

Popular posts from this blog

PowerShell Sorting by Multiple Columns

PowerShell's Sort-Object cmdlet is super useful, especially when preparing output for human consumption.  A few people have found my blog while looking for more information about its use, specifically while looking for how to sort by multiple columns (well, properties, technically).  I've never done so (much less written about it), so I hope those folks found answers elsewhere.  But, it got me curious... and it turns out that it's really easy. The Technet article on Sort-Object has the answer directly spelled out: just use commas to create a list of properties to sort by (in order to precedence).  Let's look at some examples!  First, prepare a variable with some good sortable data: $myData = get-eventlog System -newest 25 And then we can get to sorting!  Say you want to sort primarily by EntryType (Warning, Information, Error) and then by Source.  Easy-peasy: $myData | sort EntryType,Source How about if you want it to be in descending order?  Yeah, there&
Read more

Clone a Standard vSwitch from one ESXi Host to Another

One of my customers is standardizing the configurations on their HP C7000 enclosures (they've been set up at various sites by various administrators with varying involvement from the architecture team).  As such, we need to stand up some temporary resources so that we can take down the main enclosure for reconfiguration.  That's fine, we can easily ship a smaller enclosure to each site for temporary compute resources.  Some of the sites are using Standard vSwitches, so we need to be able to quickly copy the networking configuration over from their existing blades to these new, slightly different blades.  As I see it, we had 2 good options: 1) Capture a Host Profile with the desired vSwitch configuration.  Delete every other component of the Host Profile so that only the networking section is applied; design the new ESXi hosts so that the vSwitches'll work with the old vmnic-to-vswitch configurations. 2) Write a script to clone the vSwitch from ones ESXi host to another.
Read more

Deleting Orphaned (AKA Zombie) VMDK Files

A problem that most Virtualization Administrators need to deal with is Orphaned VMDK files (or Zombie VMDK files, as some people call them).  These are Virtual Machine hard drive files that are just hanging out, taking up storage, but are attached to no VMs.  How can this happen?  Well, the most common way is when an administrator needs to delete a VMDK but isn't quite ready to commit... so, after pressing "remove", they select "remove from virtual machine" rather than "remove and delete files".  The intent is always good: "I want to be able to restore this if it turns out to be necessary... so I'll just come back and delete it next week if nothing breaks!"  But, of course, next week something else happens and the file doesn't get deleted.  After a little while, it turns into "which files did I rename, again?" and nothing seems to happen. So, how do you deal with these orphaned files?  Well, a few years ago I found a scrip
Read more