How can use /8 network for AzureStack HCI deployment without vLAN

@Ng, Ronald

I cross checked with internal team on this ask and below are few considerations on this.

• Azure Stack HCI uses RDMA and a significant portion of those deployments will require Data Center Bridging. DCB requires a VLAN to set the priority tagging required to make this traffic "reliable."
• Subnetting and VLANs exist for a reason. A /8 network can have up to 16,777,216 (I think I got all the 7's in there). That's a lot of broadcast messages that can flood a system. I don't know your exact setup, but this isn't a wise practice and so we don't allow to do that via WAC.
• If you're building this in a lab environment (as you stated), you'll want your lab environment to look like production otherwise these aren't really valid tests from a network perspective.

To work around, you can try one of the following options.

• Create a cluster from PowerShell, using New-Cluster cmdlet. (Or use alternative tool such as System Center.)
• Create a cluster with the desired network address but smaller size. Adjust subnet mask manually after deployment. (Be aware that cluster might behave weirdly while you’re in the middle of making the change, as only a subset of nodes would have new settings, and that might cause a confusion in intra-cluster communications.)

Note:
This isn't a limitation of WAC as much as a protection against what is more likely a misconfiguration or bad practice. WAC's goal is to ensure that at the end of the wizard, there is a high likelihood of a working cluster that can reliably run S2D and the VMs on top of it. Yes, it is possible that a /8 network can do that without VLANs, but it's extraordinarily unlikely. At the root, that's why using a /8 is not allowed via WAC. You can of course work around this if you know better (via PowerShell); but WAC isn't going to help you setup that configuration because there are a lot of potential issues that we can't check for proactively.

Hope this helps.
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