VM IP Address network size

[ksherwood]

Hello all,

                  I have a quick question on setting up VM's on the cisco UCS or any other virtual server type system.

Our server team claim that a dedicated class 'C' address range set up in DHCP is filling quickly and will soon be fully used up by an increasing number of virtual servers.

So our network team has suggested that we could just set up another routed VLAN to accommodate any further growth.

Our server team then claim that managing other VLANs is too hard and just want a huge supernet range instead.

I'm pretty sure that a large supernet is not a best practice for many reasons but can anyone back up this theory and maybe point out a document that reports this formally.

Thanks in advance.

[Reza Sharifi]

Hi,

It all depend on how many VMs they are deploying.  Each VM needs an IP address. So, if they are deploying 500 VMs, one /24 subnet is not enough.  Depending on how they are dividing the applications based on security and/or classification, they may need 2, 3 or even 4 subnets.

I have seen VM environments with 50 or 60 vlan/subnets and VM environments with 2 or 3 vlans/subnets.

HTH

[ksherwood]

Yes Reza, but they are saying that it is too hard to create multiple virtual switches to accommodate many subnets/VLANs as their server requirements grow. On the extreme side of the argument they are saying why not just give us 65,000 addresses and then we only need one virtual switch configured within their VM environment.

I am saying that that is not best practice and the limit should be a /24 subnet, and if they need more subnets then create more virtual switches per VLAN and so be it.

I'm not a VM guru so I'm just guessing that you must be able to manage multiple VLANs or subnets without having a single supernet which goes against IP addressing best practice ???

[Walter Dey]

I think the server guys still mandate a flat network, because vmotion and live migration asked actually for this for the last 10+ years; now with vSphere V6, vmotion is supported over L3 boundaries; however, if your server requires a static address, you have a problem.

This is exactly the use case, that ACI is solving, L2 over L3, VXlan is your friend.

[Walter Dey]

I think the server guys still mandate a flat network, because vmotion and live migration asked actually for this for the last 10+ years; now with vSphere V6, vmotion is supported over L3 boundaries; however, if your server requires a static address, you have a problem.

This is exactly the use case, that ACI is solving, L2 over L3, VXlan is your friend.