What is the correct statement about IPsec and IKE? (Choose 3 Answers)

What is the correct statement about IPsec and IKE? (Choose 3 Answers)
A . IPsec has two ways to establish an alliance, one is manual, one is IKE auto-negotiation (isakmp).
B . IKE aggressive mode can choose to negotiate the IP address or ID of the initiator to check the find the corresponding authentication and complete the negotiation finally.
C . The NAT across function deletes the verification process of UDP port number during the IKE negotiation. At the same time, the discovery function of the NAT gateway device in the VPN tunnel is implemented. That is, if the NAT gateway device is discovered, then the after IPsec data transmission use UDP encapsulation.
D . IKE security mechanisms include DH Diffie-Hellman switching and key distribution, perfect forward security (PFS) and SHA1, etc. encryption algorithm.

Answer: ABC