Spreading Datacentre across differnet subnets

[imsorrydave]

Hello,

My organisation is looking to migrate from a single ESX 2.5 host to a 2+ host VI3 datacentre spread over two physically seperate locations.

We are being advised that to achieve this (from a networking POV) the hosts at each site will have to be on different IP subnets.

My question is this:

Is this networking configuration supported by VMware for Vmotion/HA/DRS, and if so, how do people deal with having to change the IP address on the guest VM OS and Application?

Thanks in advance,

David

[VMKR9]

This works fine, you just set up your HA/DRS clusters around the new subnets. As for changing the IPs in guest vms its just a case of manually changing them, unless your apps are hardcoded to specifics IPs you shouldn't have a problem.

[TomHowarth]

why does this have to be the case. you could have same VLANs on both sites in a properly designed envrionment.

[Texiwill]

Hello,

Tom is this what you meant?

If you have a data center across multiple subnets and the same VLANs, you would need to somehow bridge the VLANs from subnet to subnet using some form of physical means. If your edge switches/routers support this type of trunking then all should work just fine. However, if you are not using VLANs or the same VLANs then you need to route the traffic and then would have to fix up IPs on a vMotion, etc.

I like the idea of using VLANs so that I do not have to fix up the IPs....

Another option is to setup IP aliases for each subnet within the VMs and hosts and then have a watchdog that flips the default route within the VM.

Everything eventually depends on the cost of the solution.

Best regards,

Edward

Message was edited by:

Texiwill

[imsorrydave]

Thanks for your replies.

Please forgive my ignorance of the networking topics, it's not really my area, I'm from a server / desktop background.

Our comms guys original intention was to give us access to the same VLAN at both sites, but now, because of a design change which has been forced upon them, they are are unable to provide this.

This leaves us with the option you mention of routing the traffic and "fixing" the IP's. Can you clarify what you mean by fixing please?

David

[Texiwill]

Hello,

When you move a VM from one subnet to the other, the ip address is incorrect for the new subnet. You would need to change the IP appropriately for the new subnet... Hence fixing the ips to be correct for each subnet.

Best regards,

Edward

[ahoogerhuis]

Tell your network guys that you want a link that is able to support "q-in-q" (Aka metro ethernet and a variety of other monikers), it's basically the abilty to run 802.1q tagged ethernet frames across the providers infrastructure (usually MPLS in some form here).

This allows you to have the same VLAN for your vMotion net, etc on both sites, and as an added benefit, moving machines from one site to the other is now a non-issue.

-A

[imsorrydave]

Thanks Edward,

I guess I was just being a little slow that day.

Just to confirm then, I can have one ESX host on one subnet and one on another and the VMotion will take place fine, but the guest OS / Application will need to be reconfigured for the new subnet after a successful VMotion?

David

[Texiwill · Accepted solution]

Hello,

That is correct. You can write a small script that will run within the VM and do this for you. It would be my suggestion.

Best regards,

Edward

[imsorrydave]

Thanks for your reply.

I checked with my colleagues and they had intended to use 802.1q before the design change was forced upon them. Now they are unable to provide this.

Dave