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How To Determine Vmkernel Interface MAC Address

It becomes incredibly difficult with multiple layers of virtualization to sometimes know what is what. One particular area where this becomes a challenge is determining MAC addresses of the ESXi components. Specifically, determining what MAC addresses compose the vmkernel interfaces can become challenging with virtual switches provided by the host and multiple host-based network services on that switch.

While this can be done with PowerCLI or SSH, I'm a fan of getting this point information in the vSphere Client.

The first step would be to clearly identify the MAC addresses of the network adapters of the host, which is done in the network adapters section of the vSphere Client. Fig. 1 shows the three interfaces on a ProLiant ML 350 host in my lab.

The MAC addresses of the host interfaces, shown in the vSphere Client.

Figure 1. The MAC addresses of the host interfaces, shown in the vSphere Client. (Click image to view larger version.)

When it comes to the vmkernel interface, which is the software stack on the ESXi host that interacts with the vCenter Server and performs additional duties such as doing vMotion events and providing the iSCSI initiator service in certain configurations, the plot thickens.

With a default installation of ESXi, the vmkernel interface is a logical node on a default virtual switch, which will assume an IP address using the MAC address of the first interface it can connect to. Should additional vmkernel interfaces be added, ESXi will create a MAC address not based on the hardware interface type on the host. Fig. 2 shows a secondary vmkernel interface on the same ProLiant ML350 host, yet uses a different MAC identifier string.

The MAC address of additional vmkernel interfaces won't use the host MAC identifier.

Figure 2. The MAC address of additional vmkernel interfaces won't use the host MAC identifier. (Click image to view larger version.)

With virtualization comes many levels of abstraction, and the vmkernel interface is an important aspect of the vSphere implementation. The MAC address may be needed for QoS priorities on the switching infrastructure or possibly IP reservations, firewall rules and more.

How do you manage the vmkernel interface MAC address? Share your strategies here.

Posted by Rick Vanover on 06/11/2012 at 12:48 PM


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