vMotion between hosts on different subnets

[combsct]

Before we start, I'm a Network Engineer, not a Server Guru, so please bare with me

Is it possible to vMotion a VM, from a host on one IP network, to another host, on a different IP network?

Example:

Datacenter 1 - ESX Server 10.1.1.1/24 with VM's in the 10.1.2.0/24

Same City, different site, 10 Gb fiber link between facilities 2ms latency

Datacenter 2 - ESX Server 10.2.1.1/24 with VM's in the 10.2.2.0/24

Scenario:

vMotion a VM from the 10.1.2.0/24 network, to the 10.2.2.0/24 network where the VM, upon arrival on the Datacenter 2 ESX server, now uses a 10.2.2.0/24 IP address.

Any guidence toward a whitepaper or guide would be greatly appreciated.

Thank you all for your time.

-Chris

Network Engineer

Press Ganey Associates

[Troy_Clavell]

assuming all networking is setup exact on both source and destination ESX Hosts, yes you can vMotion.  If the proper networking is not setup, you'll receive an error message when trying to select your destination host.

http://www.vmware.com/files/pdf/VMware-VMotion-DS-EN.pdf

[ShantanuVCP]

vMotion uses Vmkernel ports to perform a hot migration from one host to another and in case of cold migration it uses Management ports.

Now when we say that the hosts are different subnet, we mean the service console ports of each host are configured on a different subnet or on a different VLAN. So if we ensure that all the different VLAN are accessible to each other and also all the different VLAN's are configured on each Virtual switch which in turn would be connected to each individual ESX host, then I am sure vMotion between different subnets should be possible. Offcourse appropriate trunking should be done at the respective trunk port.

[combsct]

The idea would be to have the two ESX servers on different subnets, that do not have a layer 2 adjacency. The servers would only be able to talk to each other over a layer 3 segment.

But from the sounds of things, vMotion requires the source and destination servers to share a common layer 2 subnet. Does that sound about right?

-Chris

[sflanders]

I think a better way to put it is that VMware only supports it via L2 though L3 should work. See: http://www.yellow-bricks.com/2010/08/19/layer-2-adjacency-for-vmotion-vmkernel/

[bulletprooffool · Accepted solution]

vMotion is possible between hosts on different subnets, but unless your PortGroups presented to the VMs are on the same subnets, you'll end up dropping the VM on a different VLAN and IP addressing will fail.

There are ways around this, you could script the IP change / present multiple IPs to the VM / or use DHCP reservations, but you'll need to ensure that DNS records etc are updated.

If you have some sort of load balancer, you could in theory load balance accross 2 IPs hosted on the same VM, to resolve network ip issues, though ultimately, you'll want a stretched VLAN to cover VM port groups.

Good luck

[combsct]

Thank you all for the information and answers!

-Chris