igorpa2
Contributor
Contributor

[HELP]2(two) virtual nics with same MAC Address

Hello guys, i have an VMware vSphere 6 Hypervisor and i´m having a problem with my Virtual Machines where, when i add two or more virtual nics in the VM´s, when the VM come UP, simply the vSwitch configure the same MAC Address to the NICS running only one network card in my network. If i ping to the network cards, only one NIC respond the package and only when i turn off the network card that is responding, the other card starts to run and respond to pings. The NICS are automatically configurated and i´m not configure anything more. i Think this is a bug ? Or have one thing that i can do and i did not do ? Thanks for any help.

Pictures about what i said.

Printscreen on NIC Configured:

Image 1.jpeg

Printscreen on what vSwitch is showing:

Image 2.jpeg

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10 Replies
igorpa2
Contributor
Contributor

Anyone ?

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ThompsG
Virtuoso
Virtuoso

Hi igorpa2 and welcome to the community!

Check the VMs vmx file for the lines that start with ”ethernet”. You should have two that look like ethernetN.generatedAddress and they should be different.

If you attach the vmx file here then we can review to confirm if you like. Don’t post the contents but upload the file please Smiley Happy

Kind regards.

igorpa2
Contributor
Contributor

Hello ThompsG​, thanks for the reply, the file is attached.

Thank you very much for supporting.

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Raj1988
Enthusiast
Enthusiast

The MAC is different from the vmx. So there seems to be no issue here.

ethernet1.generatedAddress = "00:0c:29:ff:13:3d"

ethernet0.generatedAddress = "00:0c:29:ff:13:33"

For Duplicate MAC:- VMware Knowledge Base

Regards,

AJ

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igorpa2
Contributor
Contributor

But why i can only ping to the second network card, when i switch off the first?

And why the vSwitch are showing the same MAC adress for both network cards?

It´s very strange to me, because if are okay and no issue, I could ping to the two network cards.

I looked at this link that you sent me, but it addresses and treats to the case where two or more vCenter Server is used and not my case, which is all within it.

Regards.

SMI-admin
Contributor
Contributor

Did you ever get this sorted out?  I'm having the same issue, BUT the vm screen shows different mac addresses, and the vswitch shows only one of those mac addresses on both port groups (different vlans - like you're screenshot).  Uhg!

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pwolf
Enthusiast
Enthusiast

Have you looked into the network card configuration on your VM. Maybe you have overwritten the MAC settings of ESXi with a custom MAC inside of your VM. Almost all modern adapters let you change the MAC from the OS adapter driver settings.

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SMI-admin
Contributor
Contributor

Nothing was overwritten.  The vSwitch display still has the wrong mac address displayed 'thing' going on I guess...

Once I was able to get onsite, I was able to check ARP tables on the switch ports.  Discovered the 2nd nic from the Host was connected to the wrong switch port - which didn't have the vlans provisioned....   Swapped back to correct port and all good... 

Not sure who would have moved it, but it was probably me... 😉  Outdated documentation, etc, etc ... 

Thanks for the input though!  Mystery solved!

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pwolf
Enthusiast
Enthusiast

Good, that you sorted it out.

But you obviously had not the same problem as the original poster, who had 2 different virtual NICs connected to just one physical NIC. But of course wrong VLAN settings on switches are always a wide field for network errors.

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SMI-admin
Contributor
Contributor

Actually from the screenshots, that's exactly what I had going on.  2 vmnics on one physical nic (minus one) separated by vswitches that showed the same mac address on both (and still does).  Yes, I had 2 load balanced, but the vsphere client still reported exactly the above.

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