Compared with IKEv1, IKEv2 simplifies the negotiation process and is much more efficient.
IKEv2 defines three types of exchanges: initial exchanges, CREATE_CHILD_SA exchange, and INFORMATIONAL exchange.
As shown in Figure 120, IKEv2 uses two exchanges during the initial exchange process: IKE_SA_INIT and IKE_AUTH, each with two messages.
IKE_SA_INIT exchange—Negotiates IKE SA parameters and exchanges keys.
IKE_AUTH exchange—Authenticates the identity of the peer and establishes IPsec SAs.
After the four-message initial exchanges, IKEv2 sets up one IKE SA and one pair of IPsec SAs. For IKEv1 to set up one IKE SA and one pair of IPsec SAs, it must go through two phases that use a minimum of six messages.
To set up one more pair of IPsec SAs within the IKE SA, IKEv2 goes on to perform an additional two-message exchange—the CREATE_CHILD_SA exchange. One CREATE_CHILD_SA exchange creates one pair of IPsec SAs. IKEv2 also uses the CREATE_CHILD_SA exchange to rekey IKE SAs and Child SAs.
IKEv2 uses the INFORMATIONAL exchange to convey control messages about errors and notifications.
Figure 120: IKEv2 Initial exchange process
