https://www.cisco.com/c/en/us/td/docs/security/asa/asa96/configuration/vpn/asa-96-vpn-config/vpn-remote-access.html The IPsec-proposal configuration option is used to specify the encryption, integrity, and authentication algorithms that will be used in the IPsec protocol. In the case of IKEv2-based VPN, this option is used to configure the IPsec security associations (SA) that will be established between the VPN client and the VPN gateway during IKEv2 negotiation. IKEv2 uses IPsec as its underlying encryption and authentication protocol, so the IPsec-proposal configuration is essential to establishing a secure VPN tunnel using IKEv2