Use rollback to prevent accidental misconfiguration of management networking and loss of connectivity to the host by rolling back to a previous valid configuration.

In vSphere 5.1, rollback is enabled by default. However, you can enable or disable rollbacks at the vCenter Server level.

Several networking events can trigger a rollback. The events are grouped into the following categories:

Host networking rollbacks (virtual switches or network system)

Distributed switch rollbacks

Host networking rollbacks occur when an invalid change is made to the host networking configuration. Every network change that disconnects a host also triggers a rollback. The following changes to the host networking configuration are examples of what might trigger a rollback:

Updating the speed or duplex of a physical NIC.

Updating DNS and routing settings.

Updating teaming and failover policies or traffic shaping policies of a standard port group that contains the management VMkernel network adapter.

Updating the VLAN of a standard port group that contains the management VMkernel network adapter.

Increasing the MTU of management VMkernel network adapters and its switch to values not supported by the physical infrastructure.

Changing the IP settings of management VMkernel network adapters.

Removing the management VMkernel network adapter from a standard or distributed switch.

Removing a physical NIC of a standard or distributed switch containing the management VMkernel network adapter.

If a network disconnects for any of these reasons, the task fails and the host reverts to the last valid configuration.

Distributed switch rollbacks occur when invalid updates are made to distributed switch-related objects, such as distributed switches, distributed port groups, or distributed ports. The following changes to the distributed switch configuration might trigger a rollback:

Changing the MTU of a distributed switch.

Changing the following settings in the distributed port group of the management VMkernel network adapter:

Teaming and failover

VLAN

Traffic shaping

Blocking all ports in the distributed port group containing the management VMkernel network adapter.

Overriding the policies above for the distributed port the management VMkernel network adapter is connected to

If an invalid configuration for any of the changes occurs, one or more hosts might be out of synchronization with the distributed switch.

If you know where the conflicting configuration setting is located, you can manually correct the setting. For example, if you migrated a management VMkernel network adapter to a new VLAN incorrectly, the VLAN might not be trucked on the physical switch. When you correct the physical switch configuration, the next distributed switch-to-host synchronization will resolve the configuration issue.

If you are not sure where the problem exists, you can rollback the distributed switch or distributed port group to a previous configuration. You perform both of these steps manually.