Feature pages are design documents that developers have created while collaborating on oVirt.

Most of them are outdated, but provide historical design context.

They are not user documentation and should not be treated as such.

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Autodefine External Network


This feature extends Provider Physical Network adding support for auto-defined external network connected to physical ones. With this feature implemented, when a physical VM network is created, Engine automatically creates an external network based on it, and connects the external network to the physical one. This makes it easier to use the former feature, and helps oVirt to model host networks and VM networks separately.

Related patches can be found on gerrit topic:autodefine.


Benefit to oVirt

Provider Physical Network is useful for users who would like to manage their network via SDN (such as OVN or Neutron) yet have near-native performance. However, without auto-define feature, such admin would have to create a physical network (and attach it to hosts), create an external network, and remember to connect this two networks together. Autodefine helps reducing these administrative tasks. In an OvS cluster with an external provider attached, the external network is automatically created and connected to the physical one.


Cluster has to be configured with switch type OvS and valid external provider. The user needs to make sure that connection to external provider is valid.


  • With OvS switch type in cluster, only external networks are allowed to be attached to the VM interface via UI.

  • Physical network linked to any external network cannot be removed. This is for keeping the consistency of database. In the future we might add a way to remove all dependent external networks with physical one.

  • The switch type of existing clusters cannot be changed (from Linux bridge to OvS or vice versa) via UI. Thus, we currently do not need to worry about auto-defining external networks on top of existing physical networks.

  • Currently, updating the physical network will not update the auto-defined external network. This might change in the future.

  • VMs will be scheduled only on hosts that does have attached linked physical network to one of it’s interfaces. Same rule applies for hotplug of VM interfaces.

Detailed description

Creating of new physical network

When creating new network choose its name. Check the VM network. If vlan tagging is needed, check the Enable VLAN tagging and put the tag into the field. Please note that auto-define can be triggered only on top of network that is not marked as external.

Creation of physical network

After confirmation if all conditions were met, the external network connected to the physical one, will be created simultaneously. The auto-defined external network is named external_name_of_physical_network (The physical network name might be shortened so that auto-defined network name is not bigger than 256 characters).

Auto-define network created

In case there are clusters with different default external providers in the data center the Engine will create multiple external networks for every provider and add a number behind to this auto-defined network name.

Please note that all hosts running VMs connected to the external network has to be attached to the physical network.



  • A new query GetAllVmNetworksByClusterId that returns only VM networks is added. For Cluster with OvS switch type, this query returns only external networks.

  • Validations for all limited operations with auto-defined external network and its linked physical network. According to Autodefine External Network - Limitations

  • Added new command AutodefineExternalNetwork. This command is triggered every time a new network is created. The command validates the incoming network and its parameters. Then it finds all clusters with OvS switch type attached to incoming network and clusters external providers. The command continues with creating new external network and connecting it to the incoming physical network and attaching to clusters. The command might create multiple external networks, one for each external provider in the data center. The command will automatically create vNIC profile, with permissions given only to the user that created the physical network.

  • Added new function getAllExternalNetworksLinkedToPhysicalNetwork into NetworkDao which returns list of all external networks linked to provided physical network.


Testing should cover:

  • Addition/Removal new physical network.

  • Physical network linked to external network cannot be removed.

  • Only external networks can be used for VM interfaces.

  • Cluster switch type cannot be updated to OvS for existing cluster.

  • VMs cannot be scheduled on hosts without attached physical network linked to auto-define network.

  • Interface cannot be hotplugged onto a VM that runs on host that is not attached to physical network which is linked to auto-define network.