#Network mac address multiple mac#
Of these six addresses, three of them are being used by vmk0 (one per lab host) and the other three are being used by IPMI.ĭid you notice that vmnic0’s MAC address (00:25:90:73:07:ab) appears on the list as being reachable via port gi5? Great – so how do we know if this is being learned via traffic from vmk0 or vmnic0? Validating The MAC Address RelationshipĪnswer: Let’s ask LLDP. According to the switch, vmnic0 is plugged into port gi29. I’ve highlighted the non-VMware OUI MACs in yellow (ignore the final one on Po8 that’s the VLAN interface on my upstream switch). I’ll pull up a MAC address table from the switch that ESX1 is using, specifically on VLAN 20 (lab stuff). I’ve also verified that vmk0 is using the same MAC address as vmnic0. Here’s a look at the four network adapters being used by ESXi host ESX1. These tend to have their own MAC addresses in most cases. A few exceptions: out of band interfaces (iLO, DRAC), IPMI, PXE, and other system connections that are referenced outside of the hypervisor. Once vmk0 clones the MAC address, you’re pretty much done with ever seeing a MAC address from your NICs on your upstream switch. The same goes for all vmkernel interfaces other than vmk0, which clones the MAC from the first vmnic it finds during installation to avoid using a VMware OUI that might already be in use. Virtual machines have their own virtual NICs that use VMware’s OUI (00:50:56.x.x.x), and so the VM’s own MAC would appear in the source portion of the frame header as it leaves the ESXi host. It’s perfectly normal, trust meīy and large, the BIA of your physical NICs are not used by any frames being generated by the ESXi host.
![network mac address multiple network mac address multiple](http://www.highteck.net/images/255-Ethernet-ARP-process2.jpg)
The red herring was finding that vmk0 used the same MAC address as a hardware NIC – but let’s go deeper into why this is both normal and not the cause for duplicate MAC alarms.
![network mac address multiple network mac address multiple](https://www.tuc.gr/fileadmin/_migrated/pics/1_03.jpg)
Recently, a related question popped up in the VMTN forums from a user posting about a duplicate MAC address alarm – you can read about that here. In fact, this is something that Pantol and I cover in our standard switch chapter of Networking for VMware Administrators ( here’s an excerpt). If you’ve ever looked a little more closely at the MAC address used by vmkernel interface 0 (vmk0), you may have noticed that it uses the burned-in address (BIA) of one of your network adapters (usually vmnic0). 2 Validating The MAC Address Relationship.