Note: IKE V1 Phase 1 mainly negotiates the following three tasks: First, negotiate the parameters used to establish IKE SA: encryption algorithm, integrity verification algorithm, identity authentication method and authentication word, DH group, IKE SA life cycle, etc. . These parameters are defined in the IKE security proposal. The second is to use the DH algorithm to exchange information related to the key (the material for generating various keys), and the peer devices can use each of the key information to generate a symmetric key for ISAKMP message encryption and verification. The third is to verify each other's identity and use a pre-shared key or digital certificate to verify identity.