When choosing a port binding type, consider how you want to connect your virtual machines and virtual network adapters to a vDS and how you intend to use your virtual machines. Port binding type, along with all other vDS and port group configuration, can be set only through vCenter Server.

Note: For more information about using port binding in iSCSI adapter configuration, see Considerations for using software iSCSI port binding in ESX/ESXi (2038869).

VMware ESXi 4.1.x Embedded
VMware vSphere ESXi 5.0
VMware vCenter Server 5.1.x
VMware vCenter Server 5.0.x
VMware vSphere ESXi 6.5
VMware ESXi 4.1.x Installable
VMware vCenter Server 4.0.x
VMware vCenter Server 6.0.x
VMware vCenter Server 6.5.x
VMware ESX 4.1.x
VMware vCenter Server 5.5.x
VMware vSphere ESXi 5.5
VMware ESX 4.0.x
VMware ESXi 4.0.x Embedded
VMware ESXi 4.0.x Installable
VMware vSphere ESXi 5.1
VMware vCenter Server 4.1.x
VMware vSphere ESXi 6.0

Types of port binding on a Distributed Switch

These two types of port binding determine how ports in a port group are assigned to virtual machines:

• Static Binding
• Ephemeral Binding

Static binding

When you connect a virtual machine to a port group configured with static binding, a port is immediately assigned and reserved for it, guaranteeing connectivity at all times. The port is disconnected only when the virtual machine is removed from the port group. You can connect a virtual machine to a static-binding port group only through vCenter Server.

Note: Static binding is the default setting, recommended for general use.

If vCenter to host communication is lost, VMs currently running on port groups with static binding will continue communication as normal because they have already been assigned their port assignments from vCenter. If vCenter to host communication is lost, VMs will not be able to be reconfigured to static (also known as non-ephemeral) port groups on the vDS because vCenter is unavailable to give the VM a port binding. In this instance, the user will see the following error:

Addition or reconfiguration of network adapters attached to non-ephemeral distributed virtual port groups is not supported.

The VMs will not be able to be reconfigured or powered on until vCenter to host communication is back. The work around for these VMs is to add them to a standard switch if vCenter to host communication is not possible. 

Ephemeral binding

In a port group configured with ephemeral binding, a port is created and assigned to a virtual machine by the host when the virtual machine is powered on and its NIC is in a connected state. When the virtual machine powers off or the NIC of the virtual machine is disconnected, the port is deleted.

You can assign a virtual machine to a distributed port group with ephemeral port binding on ESX/ESXi and vCenter, giving you the flexibility to manage virtual machine connections through the host when vCenter is down. Although only ephemeral binding allows you to modify virtual machine network connections when vCenter is down, network traffic is unaffected by vCenter failure regardless of port binding type.

Note: Ephemeral port groups are generally only used for recovery purposes when there is a need to provision ports directly on a host, bypassing vCenter Server. For example, the management vmkernel port group and the vCenter VM's port group.

VMware Validated Designs, for example, use these for the Management Domain to help allow flexibility in the management cluster in the event of a vCenter outage. If a Management Cluster is not used, then it is recommended to create an ephemeral port group on the VDS for Management workloads (including vCenter), allowing them to attach to it during a vCenter outage.

There are various things to consider with ephemeral port groups, as detailed below. The below reasons are why static binding is the default on distributed switch port groups (only change to ephemeral binding for vCenter, management, etc.)

Performance

Every operation, including add-host and virtual machine power operation, is slower comparatively because ports are created/destroyed in the operation code path. Virtual machine operations are far more frequent than add-host or switch-operations, so ephemeral ports are more demanding in general.

Non-persistent "ephemeral" ports

Non-persistent (that is, "ephemeral") ports port-level permissions and controls are lost across power cycles, so no historical context is saved."
 

Virtual Machine Error: "Addition or reconfiguration of network adapters attached to non-ephemeral distributed virtual port groups is not supported"

This error will generate if trying to connect a virtual machine to a distributed port group that uses Static binding while the vCenter is not connected to the network. As stated above, you can connect a virtual machine to a static-binding port group only through vCenter Server. 

If vCenter itself is also on a vDS static bound port group, please follow this KB to get it connected again: vCenter network connectivity lost - Recover vCenter network when connected to a Distributed Switch (83906)