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On my hundreds bare metal, I was unable to collect any MAC address. iLO not seeing external NIC on PCI.
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PS C:\Windows\system32> Get-HPiLONICInfo -Username $iLoUser -Password $iLoPass -Server 10.255.255.201


IP             : 10.255.255.201
HOSTNAME       : iLoNoOS.domain.local
STATUS_TYPE    : OK
STATUS_MESSAGE : OK
iLO            : @{IP_ADDRESS=10.255.255.201; LOCATION=Embedded; MAC_ADDRESS=9c:xx:xx:xx:xx:1b; NETWORK_PORT=iLO Shared Network Port; PORT_DESCRIPTION=iLO Shared Network Port; STATUS=OK}
NIC            : {@{IP_ADDRESS=N/A; LOCATION=Embedded; MAC_ADDRESS=9c:xx:xx:xx:xx:18; NETWORK_PORT=Port 1; PORT_DESCRIPTION=N/A; STATUS=Unknown}, @{IP_ADDRESS=N/A; LOCATION=Embedded;
                 MAC_ADDRESS=9c:xx:xx:xx:xx:19; NETWORK_PORT=Port 2; PORT_DESCRIPTION=N/A; STATUS=Unknown}}


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I can see external NIC detail only after deployed OS.
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PS C:\Windows\system32> Get-HPiLONICInfo -Username $iLoUser -Password $iLoPass -Server 10.255.255.209


IP             : 10.255.255.209
HOSTNAME       : iloname.domain.local
STATUS_TYPE    : OK
STATUS_MESSAGE : OK
iLO            : @{IP_ADDRESS=10.255.255.209; LOCATION=Embedded; MAC_ADDRESS=9c:ff:ff:ff:ff:ff; NETWORK_PORT=iLO Shared Network Port; PORT_DESCRIPTION=iLO Shared Network Port; STATUS=OK}
NIC            : {@{IP_ADDRESS=N/A; LOCATION=Embedded; MAC_ADDRESS=9c:ff:ff:ff:ff:ff; NETWORK_PORT=Port 1; PORT_DESCRIPTION=HP Ethernet 1Gb 2-port 361i Adapter; STATUS=Unknown}, @{IP_ADDRESS=N/A;
                 LOCATION=Embedded; MAC_ADDRESS=9c:ff:ff:ff:ff:ff; NETWORK_PORT=Port 2; PORT_DESCRIPTION=HP Ethernet 1Gb 2-port 361i Adapter; STATUS=Unknown}, @{IP_ADDRESS=10.255.255.210;
                 LOCATION=Slot 1; MAC_ADDRESS=64:51:aa:aa:aa:b1; NETWORK_PORT=Port 3; PORT_DESCRIPTION=HP Ethernet 10Gb 2-port 530T Adapter; STATUS=OK}, @{IP_ADDRESS=N/A; LOCATION=Slot 1;
                 MAC_ADDRESS=64:51:aa:aa:aa:b2; NETWORK_PORT=Port 4; PORT_DESCRIPTION=HP Ethernet 10Gb 2-port 530T Adapter; STATUS=Unknown}}