Lightweight Directory Access Protocol (LDAP) is an open, vendor-neutral protocol for accessing and maintaining distributed directory information, such as user accounts, groups, and other identity data, over a network. LDAP directories are commonly used to centralize user and group management across many systems, and Microsoft Active Directory is a widely deployed implementation that also functions as an LDAP server. ONTAP can use LDAP as a name-service source to look up UNIX identity information for NFS clients—​UIDs, GIDs, and group memberships—​and to support user mapping and other identity lookups for SMB clients. Using LDAP for name services provides greater security and scalability than local files alone, particularly in environments using NFSv4 or later.

Prior to ONTAP 9.20.1, consistent UID/GID access across NFS and SMB required manually configuring and maintaining explicit uidNumber/gidNumber attributes for every user and group in Active Directory—​a time-consuming, error-prone process that's difficult to keep synchronized across large or multi-domain environments. ONTAP 9.20.1 introduces native SSSD support with automatic SID-to-UNIX ID conversion for NAS clients, a feature that uses a deterministic and SSSD-compatible algorithm to derive POSIX UIDs/GIDs from Windows SIDs and reverse the process to recover the original SID. It can be enabled on an SVM's LDAP client when Active Directory is the identity source, which allows ONTAP to dynamically compute consistent and reversible UNIX identities without storing any POSIX attributes in Active Directory.

Network Information Service (NIS) is a client-server directory protocol for sharing configuration information—​such as user accounts, groups, hostnames, and netgroups—​across UNIX and Linux systems on a network. NIS centralizes administration by maintaining a set of maps that clients query instead of relying on local files on every system. ONTAP can use NIS as an alternative to LDAP for NFS client authentication.