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I'm in the process of trying to decommission a few subnets which are believed to be no longer in use. When I query the mac address table on the physical switch for the vlans associated with these subnets, I see quite a few mac addresses beginning with 00:50:56 (VMware) which I am not able to correlate to any specific VM. Instead it appears that these mac addresses may be used by the vSwitch itself. Do ESXi (5.5) vSwitches themselves have their own mac address, separate and in addition to the mac addresses for the VMs? If so, what circumstances require a vSwitch to send frames from this mac address? Does this apply equally to Standard and Distributed switches?

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Do ESXi (5.5) vSwitches themselves have their own mac address

Yes.

What circumstances require a vSwitch to send frames from this mac address?

Beacon probing, RARP, a few things.

Does this apply equally to Standard and Distributed switches

Yes.

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  • Thanks - wasn't aware of beacon probing and it appears we aren't using it. Can you elaborate a bit more on rarp and 'a few things'? For rarp, my understanding is that an esx host may send frames on behalf of a VM, using the VMs source mac address, in situations such as VMotion, initial VM power-on, nic failure to move traffic to another nic. When would a host use its vSwitch mac to source these frames? – User123456 Apr 8 '15 at 17:55
  • How can one query/view the mac address used by a switch? – User123456 Apr 8 '15 at 17:56

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