Explanation: Explanations:SKIP is the no related term, we use "ISAKMP" (Internet Security Association and Key Management Protocol) as the framework for transferring keys and authenticating. "PKI" is a fundamental part of IKE functionality because it will provide the infrastructure to use digital certificates, commonly used by IKE for authentication.
"Oakley" is the protocol used to establish strong cryptography based keys used for the encryption of data.See Page 7.12 of CCSE NG Official Courseware. (VPN1-FW1 Management II NG FP-1).