vCloud Networks

13 min read

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Network Virtualization is what makes vCloud Director such an awesome tool. However, before we go full out in the next article, we need to set up the Network virtualization, and this is what we will be focusing on here.

When we talk about isolated networks we are talking about vCloud director making use of different methods of Network Layer three encapsulation (OSI/ISO model). Basically it is the same concept as was introduced with VLANs. VLANs split up the network communication in physical network cables in different totally isolated communication streams. vCloud makes use of these isolated networks to create isolated Org and vApp Networks.

VCloud Director has three different Network items:

  • An external network is a network that exists outside the vCloud, for example, a production network. It is basically a PortGroup in vSphere that is used in vCloud to connect to the outside world. An External Network can be connected to multiple Organization Networks. External Networks are not virtualized and are based on existing PortGroups on a vSwitch or Distributed vSwitch.
  • An organization network (Org Net) is a network that exists only inside one organization. You can have multiple Org Nets in an organization. Organizational Networks come in three different shapes:
    • Isolated: An isolated Org Net exists only in this organization and is not connected to an external network; however, it can be connected to vApp networks or VMs. This network type uses network virtualization and its own Network setting.
    • Routed Network (Edge Gateway): An Org Network connects to an existing Edge Device. An Edge Gateway allows defining firewall, NAT rules, as well as VPN connections and load balance functionality. Routed gateways connect external networks to vApp networks and/or VMs. This Network uses virtualized networks and its own Network setting.
    • Directly connected: These Org Nets are an extension of an external network into the organization. They directly connect external networks to the vApp networks or VMs. These networks do NOT use network virtualization and they make use of the network settings of an External Network.
  • A vApp network is a virtualized network that only exists inside a vApp. You can have multiple vApp networks inside one vApp. A vApp network can connect to VMs and to Org networks. It has its own network settings. When connecting a vApp Network to an Org Network you can create a Router between the vApp and the Org Network that lets you define DHCP, Firewall, NAT rules and Static Routing.

To create isolated networks, vCloud Director uses Network Pools. Network pools are collection of VLANs, PortGroups and VLANs that can use L2 in L3 encapsulation. The content of these pools can be used by Org and vApp Networks for network virtualization.

Network Pools

There are four kinds of network pools that can be created:

  • VXLAN: VXLAN networks are Layer 2 networks that are encapsulated in Layer 3 packages. VMware calls this Software Defined Networking (SDN). VXLANs are automatically created by vCD, however, they don’t work out of the box and require some extra configuration in vCloud Network and Security (see later)
  • Network isolation-backed: These are basically the same as VXLANs, however, they work out of the box and use Mac in Mac encapsulation. The difference is that VXLAN can transcend routers, network isolation-backed networks can’t.
  • vSphere Portgroups backed: vCD will use pre-created portgroups to build the vApp or organization networks. You need to pre-provision one portgroup for every vApp/Org network you would like to use.
  • VLAN backed: vCD will use a pool of VLAN numbers to automatically provision portgroups on demand; however, you still need to configure the VLAN trunking. You will need to reserve one VLAN for every vApp/Org network you would like to use.

VXLANs and network isolation networks solve the problems of pre-provisioning and reserving a multitude of VLANs, which makes them extremely important. However using PortGroup or VLAN Network Pools can have additional benefits that we will explore later.

Types of vCloud Network

VCloud Director has basically 3 different Network items. An external network is basically a PortGroup in vSphere that is imported into vCloud. An Org Network is an isolated network that exists only in an Organization. The same is true for vApp Network, they exist only in vApps.

In the picture above you can see all possible connections. Let’s play through the scenarios and see how one can use them

  • Isolated vApp Network

    An Isolated vApp network exist only inside a vApp. They are useful if one needs to test how VM’s behave in a network or to test using an IP range that is already in use (e.g. Production). The downside of them is that they are isolated, meaning it is hard to get information or software in and out. Have a look at the Recipe for RDP (or SSH) forward into an isolated vApp to find some answers to this problem.

  • VMs directly connected to External Network

    VM’s inside a vApp are connected to a direct OrgNet, meaning they will be able to get IP’s from the External Network pool. Typically these VM’s are used for Production, meaning that customers choose vCloud for fast provisioning of predefined templates. As vCloud manages the IP’s for a given IP range it can be quite easy to fast provision a VM.

  • vApp Network connected via vApp Router to External network

    VMs are connected to a vApp Network that has a vApp Router defined as its Gateway. The Gateway connects to a direct OrgNet, meaning that the Gateway will be automatically be given an IP from the External Network Pool.

    These configurations come in handy to reduce the amount of “physical” Networking that has to be done. The vApp Router can act as a Router with defined Firewall rules, it can do SNAT and DNAT as well as define static routing. So instead of using up a “physical” VLAN or SubNet, one can hide away applications this way. As an added benefit these Applications can be used as templates for fast deployment.

  • VMs direct connected to isolated OrgNet

    VMs are connected directly to an isolated OrgNet.

    Connecting VMs directly to an Isolated Network normally only makes sense if there is more than one vApp/VM connected to the OrgNet. What they are used for is an extension of the isolated vApp concept. You need to test repeatedly complex Applications that require certain infrastructure like Active Directory, DHCP, DNS, Database, Exchange Servers etc. Instead of deploying large isolated vApps that contain these, you could deploy them in one vApp and connect them via an Isolated OrgNet directly to the vApp that contains your testing VMs. This makes it possible to reuse this base infrastructure. By using Sharing you even can hide away the Infrastructure vApp from your users.

  • vApp connected via vApp Router to isolate OrgNet

    VMs are connected to an vApp network that has as its Gateway a vApp Router . The vApp router gets automatically its IP from the OrgNet Pool.

    Basically, a variant of the idea before. A test vApp or an infrastructure vApp can be packaged this way and be made ready for fast deployment.

  • VMs connected directly to Edge

    VMs are directly connected to the Edge OrgNet and get their IP from the OrgNet Pool. Their Gateway is the Edge device that connects them to the External Networks through the Edge Firewall.

    A very typical setup is using the Edge Load balancing feature to load balance VM’s out of a vApp via the Edge. Another one is that the Organization is secured using the Edge Gateway against other Organizations that use the same External Network. This is mostly the case if the External Network is the internet and each Organization is an external customer.

  • vApp connected to Edge via vApp Router

    VMs are connected to a vApp network that has the vApp router as its Gateway. The vApp Router will automatically get an IP form the OrgNet, which has its Gateway the Edge.

    This is a more complicated variant of the above scenario, allowing customers to package their VM’s, secure them against other vApps or VMs or subdivide their allocated networks.

IP Management

Let’s have a look into IP management with vCloud. vCloud knows about three different settings for IP management of VM’s.

  • DHCP

    You need to provide a DHCP, vCloud doesn’t automatically create one. However a vApp Router or an Edge can create one.

  • Static – IP Pool

    The IP for the VM comes from the Static IP Pool of the network it is connected to. In addition to that DNS and Domain Suffix will be written to the VM.

  • Static – Manual

    The IP can be defined on the spot; however, it must be in the network defined by the Gateway and the Network mask of the network the VM is connected to. In addition to that, DNS and Domain Suffix will be written to the VM.

    All these settings require Guest Customization to be effective. If no Guest Customization is selected, it doesn’t work and whatever the VM was configured with as a Template will be used.

vSphere and vCloud vApps

One think that need to be said about vApps is that they actually come in two completely different versions. The vCenter vApp and the vCloud vApp.

The vSphere vApp concept was introduced in vSphere 4.0 as a container for VMs. In vSphere a vApp is essentially a resource pool with some extras, such as starting and stopping order and (if you configured it) Network IP allocation method. The idea is it to have an entity of VMs that build one unit. Such vApp then can be exported or imported using the OVF format. A very good example for an vApp is VMware Operations Manager. It comes as a vApp in an OVF format and contains not only the VMs but also the start-up sequence as well as some setup script. When the vApp is deployed the first time, additional information like Network settings are asked and then implemented. As vSphere vApp is a resource pool, it can be configured so that it will only demand resources that it is using; on the other hand resource pool configuration is something that most people struggle with. A vSphere vApp is ONLY a resource pool, it is not automatically a folder in the Folder and Template View of vSphere, but is viewed there as again as a vApp.

The vCloud vApp is a very different concept; first of all it is not a resource pool. The VMs of the vCloud vApp live in the OvDC resource Pool. However the vCloud vAppp is automatically a folder in the Folder and Template View of vSphere. It is a construct that is created by vCloud, it consists of VMs, a Start and Stop sequence and Networks. The Network part is one of the major differences (next to the resource pool). In vSphere only network information, like how IPs gets assigned to it and settings like Gateway and DNS are given to the vApp, a vCloud vApp actually encapsulates Networks. The vCloud vApp Networks are full networks, meaning they contain the full information for a given network including network settings and IP Pools. For more details see the last article. This information is kept when importing and exporting vCloud vApps.

When I’m talking about vApps in the book, I will always mean vCloud vApps. vCenter vApp, if they feature will be written as vCenter vApp.

Datastores, profiles and clusters

I probably don’t have to explain what a datastore is, but here is a short intro just in case . A Datastore is a VMware object that exists in ESXi. This Object can be a hard disk that is attached to an ESXi server, a NFS or iSCSSI mount on a ESXi host or an fibre channel disk that is attached to an HBA on the ESXi server.

A Storage Profile is a container that contains one or more Datastores. A Storage Profile doesn’t have any intelligence implemented, it just groups the Storage. However, it is extremely beneficial in vCloud. If you run out of storage on a datastore you can just add another datastore to the same Storage Profile and your back in business.

Datastore Clusters again are containers for datastores, but now there is intelligence included. A Datastore Cluster can use Storage DRS, which allows for VMs to automatically use Storage vMotion to move from one datastore to another if the I/O latency is high or the storage low. Depending on your storage backend system this can be extremely useful.

vCloud Director doesn’t know the difference between a Storage Profile and a Datastore Cluster. If you add a Datastore cluster, vCloud will pick it up as a Storage Profile, but that’s ok because it’s not a problem at all.

Be aware that Storage profiles are part of the vSphere Enterprise Plus licensing. If you don’t have Enterprise Plus you won’t get storage profiles, and the only thing you can do in vCloud is use the storage profile ANY, which doesn’t contribute to productivity.

Thin provisioning

Thin Provisioning means that the file that contains the virtual hard disk (.vmdk) is only as big as the the amount of data written to the virtual hard disk.. As an example, if you have a 40GB hard disk attached to a Windows VM and have just installed Windows on it you are using around 2GB of the 40GB disk. When using Thin provisioning only 2GB will be written to the datastore not 40GB. If you don’t use thin provisioning the .vmdk file wil be 40GB big.

If your storage vendors Storage APIs is integrated in your ESXi servers Thin Provisioning may be offloaded to your storage backend, making it even faster.

Fast Provisioning

Fast provisioning is similar to linked clones that you may know from Lab Manager or VMware View. However, in vCloud they are a bit more intelligent than in the other products. In the other products linked clones can NOT be deployed across different datastores but in vCloud they can.

Let’s talk about how linked clones work. If you have a VM with a hard disk of 40GB and you clone that VM you would normally have to spend another 40GB (not using Thin Provisioning). Using Linked clones you will not need another 40GB but less. What happens in layman’s terms is that vCloud creates two snapshots of the original VM’s hard disk. A snapshot contains only the differences between the original and the Snapshot. The original hard disk (.vmdk file) is set to read-only and the first snapshot is connected to the original VM, so that one still can work with the original VM. The second snapshot is used to create the new VM. Using snapshots makes deploying a VM using Fast Provisioning not only Fast but it also saves a lot of disk space.

The problem with this is that a snapshot must be on the same datastore as its source. So if you have a VM in one datastore, its linked clone cannot be in another. vCloud has solved that problem by deploying a Shadow VM. When you deploy a VM with Fast Provisioning onto a different datastore than its source, vCloud creates a full clone (a normal full copy) of the VM onto the new datastore and then creates a linked clone from the Shadow VM.

If your storage vendors Storage APIs is integrated in your ESXi servers Fast Provisioning may be offloaded to your storage backend, making it faster. See also recipe “Making NFS based datastores faster”.


In this article, we saw vCloud networks, vSphere and vCloud vApps, and datastores, profiles and clusters.

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