ONTAP uses the Key Management Interoperability Protocol (KMIP) to communicate with external key managers (EKMs). KMIP is an open standard that defines the communication protocol between key management systems and the encryption clients that use them. This standardization allows ONTAP to integrate with a wide variety of third-party key management servers that are KMIP-compliant, providing flexibility in choosing a key management solution for NetApp Volume Encryption (NVE) or NetApp Aggregate Encryption (NAE).

B. LDAP (Lightweight Directory Access Protocol) is used for accessing and maintaining distributed directory information services, not for key management.

C. SFTP (SSH File Transfer Protocol) is a protocol for securely transferring files over a network, unrelated to cryptographic key exchange.

D. RPC (Remote Procedure Call) is a general protocol for inter-process communication, but KMIP is the specific application-layer protocol used for this function.

- NetApp ONTAP 9 Documentation, "Configuring an external key manager." The first sentence of the overview states, "ONTAP uses the Key Management Interoperability Protocol (KMIP) to communicate with external key managers."

- NetApp ONTAP 9 Documentation, "ONTAP concepts," Security overview. This section describes the use of industry-standard protocols like KMIP for interoperability.

- OASIS, "Key Management Interoperability Protocol Specification Version 1.4." This is the official standard that defines the protocol used by ONTAP for EKM communication.