IKEv2
Phase 1
Unlike Phase 1 of IKEv1, IKEv2 does not provide options for Aggressive or Main mode. Furthermore, Phase 1 of IKEv2 begins immediately with an IKE SA initiation, consisting of only two packets (containing all the information typically contained in four packets for IKEv1), securing the channel such that all following transactions are encrypted (see
“IKEv2 cookie notification for IKE_SA_INIT”).
The encrypted transactions contain the IKE authentication, since remote peers have yet to be authenticated. This stage of IKE authentication in IKEv2 can loosely be called Phase 1.5.
Phase 1.5
As part of this phase, IKE authentication must occur. IKE authentication consists of the following:
• The authentication payloads and Internet Security Association and Key Management Protocol (ISAKMP) identifier.
• The authentication method (RSA, PSK, ECDSA, or EAP).
• The IPsec SA parameters.
Due to the number of authentication methods potentially used, and SAs established, the overall IKEv2 negotiation can range from 4 packets (no EAP exchange at all) to many more.
At this point, both peers have a security association complete and ready to encrypt traffic.
Phase 2
In IKEv1, Phase 2 uses Quick mode to negotiate an IPsec SA between peers. In IKEv2, since the IPsec SA is already established, Phase 2 is essentially only used to negotiate “child” SAs, or to re-key an IPsec SA. That said, there are only two packets for each exchange of this type, similar to the exhange at the outset of Phase 1.5.
The entire IKEv2 process is demonstrated in the following diagram: