The IPsec VPN negotiation process, managed by the Internet Key Exchange (IKE) protocol, establishes two distinct types of Security Associations (SAs). First, the IKE SA (also known as Phase 1 SA) is created. This is a bidirectional SA that secures the negotiation traffic itself, establishing an authenticated and encrypted channel between the VPN peers. Once the IKE SA is established, it is used to securely negotiate the IPsec SAs (also known as Phase 2 SAs). The IPsec SAs are unidirectional and are used to encrypt and decrypt the actual user data traffic that passes through the VPN tunnel.

A. IKE and VPND SA: vpnd is the name of the Check Point daemon (process) responsible for VPN operations, not a type of Security Association.

B. IKE SA and VPN SA: While an IPsec SA is a type of "VPN SA," this term is too generic. "IPsec SA" is the specific, standardized term for the data-plane SA.

D. VPN SA and Main SA: "Main SA" is not a standard term. It incorrectly conflates "Main Mode," one of the negotiation modes in IKEv1, with the SA itself.

1. Check Point R81.20 VPN Administration Guide: In the "Site-to-Site VPN" chapter, section "IKE (Internet Key Exchange) and IPsec", the documentation states, "The IKE negotiation generates the authenticated and encrypted channel, known as the IKE Security Association (SA). The IKE SA is used to securely negotiate the IPsec SAs. The IPsec SAs are used to encrypt and decrypt the data in the IPsec tunnel."

2. RFC 7296 - Internet Key Exchange Protocol Version 2 (IKEv2): Section 1.2, "The Two Phases of IKE," describes the process: "The first phase is the establishment of an IKE SA... The second phase involves using that IKE SA to negotiate security associations for other protocols, such as AH and ESP for IPsec." This foundational document clearly distinguishes the IKE SA from the subsequent IPsec SAs (referred to as Child SAs). (DOI: 10.17487/RFC7296)

3. Kurose, J. F., & Ross, K. W. (2021). Computer Networking: A Top-Down Approach (8th ed.). Pearson. In Chapter 8, "Security in Computer Networks," the section on IPsec and IKE explains that IKE establishes a secure channel (the IKE SA) to negotiate the parameters for the IPsec SAs that will carry the data.