During the process of establishing IPSec VPN between peers FW_A and FW_B, two types of security associations need to be established in two stages. In the first stage, _____ is established to verify the identity of the peers.[fill in the blank]*
During the process of establishing IPSec VPN between peers FW_A and FW_B, two types of security associations need to be established in two stages. In the first stage, _____ is established to verify the identity of the peers.[fill in the blank]*