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vMotion Traffic Separation

I was explaining the vMotion process to someone for the first time and explained how the migration technology transports a running virtual machine from one host to another. I love my time on the whiteboard, and I simply illustrate the process from each perspective of the core resources of the virtual machine: CPU, disk, memory and network connectivity.

The vMotion event has always been impressive, but it doesn't go without design considerations. Primarily, this traffic is not encrypted for performance reasons. VMware explains that primarily it's the way it is and not to panic. While, I'm not a security expert, I take heed of this fact and architect accordingly.

In my virtualization practice, I've implemented a layer-2 security zone for vMotion traffic. Simply put, it's a VLAN that contains the migration traffic. The TCP/IP address space is entirely private and not routed or connected in any way to any other network. The vmkernel interfaces for vMotion on each host are given a non-routable IP address in an address space that is not in use in other private networks. For example, if the hosts are in a private address space of the vmkernel interfaces for vMotion are configured on a private VLAN with an address space of Take extra steps to ensure that your private VLAN address space, the 172 network in the example above, is not in use via the routing tables of the ESX or ESXi host.

The default gateway is assigned to the service console (ESX) or management traffic (ESXi). If the private address space assigned for vMotion exists at any point in the private network, this can cause an issue if the network is defined in the routing tables, even if not in use. This is a good opportunity to check with your networking team, explaining what you are going to do for this traffic segment. I've not done it, but IPv6 is also an option in this situation.

Each time I make any comment about security and virtualization, I imagine security expert Edward Haletky shaking his head or piping in with good commentary. Anticipating what Edward would say, some security levels are not adequate with layer-2 only separation. There are two more secure options, according to Edward. The first is to use separate physical media for the vMotion traffic on a completely isolated switching infrastructure and the second is to not enable vMotion.

How do you segment virtual machine migration topic? Share your comments here.

Posted by Rick Vanover on 05/11/2010 at 12:47 PM


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