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VM MAC and UCS MAC question

Hello experts,


I am confused about something regarding MACs, I think I need some guidance seeing the big picture.


Say our VM MAC is 111(for simplicity) and it is using vnic 1 in UCS(MAC 222)


If I check MAC address table on FI I see 111 assigned to a veth..can someone provide clarity on a few things:


what do the UCS MAC pool use for?

does each VM itself have a mac or just each vmnic or b

Cisco Employee

Typical physical NICs get a from factory "burned" in MAC address which the OS will usually, but not always, use.

UCS VIC vNICs get a software assigned MAC (usually from a MAC pool) which should be unique (222).

Since UCS uses virtual NICs (vNICs) these MAC addresses (222) have to come from somewhere, hence the pool.

ESXi will often use the vNIC from the vmnic0 as the OS MAC address for management interface vmk0.


Sounds like you're using these vNICs to uplink a vSwitch for VM traffic.

Since the OS doesn't send traffic out a guest VM vSwitch the vNICs MAC (222) effectively goes unused.

The VM will send traffic from MAC (111) and the vSwitch will pass this traffic through the vNIC and up to the FI.


Most don't know but every physical switch port of every physical hardware switch has a unique MAC address. Rarely does this MAC address come into play, but it does exist. Somewhat like the vNIC has a MAC address on the vSwitch in this instance.

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