El_mont
Contributor
Contributor

The same mac on vmk0 and vmnic2

Hi all!

I have a situation that I'm not unerstand. I've ESXi 5.1 host with 4 physical nics. My Cisco alarms me that I have duplicate mac address on a port. I've cheked my VMWare configuration and see that I have 4 nics (vmnet2 - vmnet5) with different mac addresses, shown by esxcfg-nics -l, but when I enter in ESXi console esxcfg-vmknic I see alone interface with the same mac as vmnic02. May be it's a problem, my Cisco informs about? Did these interfaces (vmnic2 and vmk0) should have same macs or it's an issue?

Thank you for assistance!

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3 Replies
vfk
Expert
Expert

During initial install on the server vmkernel vmk0 interface will use the use the physical server's mac address assigned to one of the vmknic interfaces instead of a random, I think this is expected behaviours.

VMware KB:     vmk0 management network MAC address is not updated when NIC card is replaced or vmker...


and check : Networking for VMware Administrators: The vSphere Standard Switch -- VMkernel Ports | Networking for VMware Administrators: The vSphere Standard Switch | Pearson IT Cert...


Look carefully at the MAC address assigned to the vmk0 VMkernel port. Notice anything different about it when compared to other VMkernel ports? You should notice that vmk0 uses the real, burned-in address of the physical NIC instead of a randomly generated VMware MAC address. This MAC address is “seeded” at the time of the ESXi installation.
--- If you found this or any other answer helpful, please consider the use of the Helpful or Correct buttons to award points. vfk Systems Manager / Technical Architect VCP5-DCV, VCAP5-DCA, vExpert, ITILv3, CCNA, MCP
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El_mont
Contributor
Contributor

I red those articles, but have a questions yet. I have compared nics configuration on another ESXi host and see a difference. On a second host vmk0 have different mac than vmnic0 and vmnic1, and it looks like 00:50:etc... And management netwotk is accessible, and no troubles at all... This second host are connected to the same Cisco and there is no any alarms. May be I should remove vmk0 and create new with different mac? Or this interface, vmk0, must have same mac as physical interface mac?

Thank you!

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chriswahl
Virtuoso
Virtuoso

You can change the MAC address on vmk0. If vmk0 is no longer using the burned-in address, it likely means someone deleted the original vmk0 and created a new one, which pulls in a VMware OUI.

The physical network adapter MACs are neither advertised nor learned by the upstream switch. This is because zero frames are being generated with a source address of your physical network adapter.

Other than the initial address used for the installation, the hypervisor uses its own OUI for VMs and vmk ports.

VCDX #104 (DCV, NV) ஃ WahlNetwork.com ஃ @ChrisWahl ஃ Author, Networking for VMware Administrators
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