The first category of restrictions allows the administrator to configure which shares can be used anonymously:
Key: HKLM\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters\ Value: NullSessionShares (REG_SZ)
This registry value is also set by a security option, starting with Windows XP:
Network access: Shares that can be accessed anonymously
On default Windows systems, this value contains the COMCFG and DFS$ shares.
The IPC$ share does not appear in this registry value. However, it is always possible to connect anonymously to it. Restrictions for the IPC$ share are implemented at the named pipes level, as described in the next section.