Depending on the value of the following registry key Windows caches the last X numbers of logins. This makes it possible to still login to the cached AD accounts if the DC isn’t accessible.
– AD (Active Directory) … Like a database that holds the user credentials
– DC (Domain Controller) … Provides access if credentials are listed in AD
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\Current Version\Winlogon\ ValueName: CachedLogonsCount Data Type: REG_SZ Values: 0 - 50
The reason you can’t access the DC could be that the server is offline, your PC isn’t connected to a network at all or your PC is connected to another network. Keep in mind that if you can’t access the DC you won’t be able to access any components in its network.
A common scenario would be the home office. Let’s assume your PC is in your home network and not at your workplace. To get access to the network components at your workplace you have to setup a VPN connection. To setup this VPN connection you first have to login to your PC which happens on the cached credentials only. After you set up the VPN connection you are able to communicate with the DC and therefore can use the intranet components from work as usual.