If the Active Directory (AD) domain server is not reachable, you can log in to the ESXi DCUI by using user name and password authentication to perform emergency actions on the host.
In exceptional circumstances, the AD domain server is not reachable to authenticate the user credentials on the smart card because of connectivity problems, network outage, or disasters. If the connection to the AD server is lost, you can log in to the ESXi DCUI by using the credentials of a local ESXi user. This lets you preform diagnostics or other emergency actions. The fallback to user name and password login is logged. When the connectivity to AD is restored, smart card authentication is enabled again.
Loss of network connectivity to vCenter Server does not affect smart card authentication if the Active Directory (AD) domain server is available.