vSphere 5.1 and later allows you to rollback to previous networking configurations if a networking misconfiguration occurs. vSphere 5.1 also allows you to recover from any misconfiguration by connecting directly to a host to fix any networking issues through the Direct Console User Interface (DCUI). Rollback is available for use on both standard and distributed switches.
The management network is configured on every host and is used to communicate with vCenter Server and to interact with other hosts during vSphere HA configuration and operation. It is critical to centrally managing hosts through vCenter Server. If the management network on the host goes down or there is a misconfiguration, vCenter Server cannot connect to the host and therefore cannot centrally manage the vSphere infrastructure.In a vSphere standard switch (VSS) environment, you can recover from management network failure on the host by reconfiguring the host management network through a DCUI.
However, in the VDS environment, where multiple hosts are connected to a distributed switch, any network failure or misconfiguration of the management port group can potentially disconnect all hosts from the vCenter Server system. In this situation, vCenter Server cannot centrally make any changes to the VDS port group configuration and push those changes to hosts. The only way to recover from this situation is by going to individual hosts and building a VSS with a proper management network configuration. After all the hosts’ management networks have been reconfigured with a VSS and are able to communicate on the management network, vCenter Server can again manage the hosts and reconfigure the VDS.
To avoid such operational issues of going back to a VSS, if you do not have physical network interface card limitations on the hosts, you can make use of a VSS for the management network and a VDS for all other virtual infrastructure and virtual machine traffic. In such deployments, you must have at least four network adapters on the hosts: two connected to the VSS and two to the VDS.
The automatic rollback and recovery feature introduced in vSphere 5.1 addresses concerns regarding use of the management network on a VDS. First, the automatic rollback feature automatically detects any configuration changes on the management network. If the host cannot reach the vCenter Server system, it does not allow the changes to take effect. Second, you also have an option to reconfigure the management network of the VDS per host through the DCUI.
