In this long-awaited post, I’ll be looking at logical networks as far as SCVMM 2012 understands them.
A logical network defines the IP subnets and VLANs that go together. The process of doing this starts by selecting Logical Networks under Fabric > Networking and then Create Logical Network on the ribbon bar:
At this stage, all you need is a name and an optional description. Type that in and click OK. This will be the “container” for the other parts that go up to make the logical network.
If you’ve got the console showing the Overview, after a brief pause, the newly created network should appear under the IP pool usage section:
The column headings (cropped from this screenshot) show the number of IP addresses allocated for the network, total defined and number available. I’ll cover that in more detail later.
So, having created the top level object, the next step is to create the definition. To do this, you need to click on Fabric Resources in the Show section of the ribbon bar, select your new logical network and then click Create Definition in the ribbon bar.
VMM provides a default definition name (the same as the network name with _1 appended) but you can change it. You then define the host groups that this network is appropriate to. This is useful if you’ve got multiple sites with different physical hosts in each site and therefore each with their own set of logical networks – some of which might have the same address pool under certain circumstances.
On the next part, you define the IP subnets and VLANs. VMM supports both IPv4 and IPv6.
The final screen confirms the settings, you click Finish and the definition is completed.
You can stop here if you like but it is possible to go further and get VMM to be even more useful by defining an IP pool for each subnet specified in the logical network definition. Select a subnet and then click Create IP Pool in the ribbon bar.
The wizard automatically fills out what should be the correct begin and end IP address for the subnet as you’ve defined it. All you need to do on this page is enter a name for the range and an optional description. You can reduce the pool if you so wish but there is the ability to “block out” addresses from the pool so that VMM doesn’t try to use them all and this may be the better approach. One of the reasons I say this is because later on in the wizard, you need to define the default gateway and it must be an IP address within the pool definition.
This is the screen where you can reserve IP addresses, either because you have got a separate DHCP pool or because you’ve statically assigned some addresses already. You can also specify VIP addresses used by load balancers here.
On this screen, you specify one or more default gateway addresses. As the screen notes, the gateway addresses must be within the range of the IP pool. Now, I’m not sure why you would specify more than one default gateway address or how VMM would use more than one default gateway address … but you must specify at least one otherwise you can’t move on in the wizard.
You can specify a metric against each gateway address but that doesn’t clear up the “multiple default gateway” question in my mind.
On this screen, you define the DNS servers, the DNS suffix and the DNS search suffixes. Somewhat annoyingly from a user interface perspective, the screen says “DNS servers in order of use” which makes sense but when you enter them, the Insert button does just that and inserts the next entry at the top of the list, so you actually have to enter them in reverse order in order to get them entered in the correct order! Thankfully, there are move up and move down buttons.
You must specify at least one DNS server and you must specify the DNS suffix.
On this screen, you define any WINS servers in use. The screen says “Specify one or more WINS servers” but you don’t have to specify any … which is just as well given that this is an old technology that isn’t needed by newer products and operating systems.
The final screen summarises the settings, you click Finish and the IP pool is created.
What the definition of an IP pool does for you is allows VMM to automatically assign IP addresses when you create hosts or new VMs. It can do this because host profiles can specify a logical network to be used.
You can also manually associate a network adapter with a logical network. The UI for this is a bit buried so I’ll document it here. Start by right-clicking a host and choosing Properties. In the window that opens, select Hardware on the left hand side, and a network adapter in the centre column. On the right hand side, you’ll then see the network adapter properties, including the opportunity to select as many logical networks as are appropriate for this adapter: