Aggressive Mode Key Exchanges
Peers that want to participate in the IPSec session must authenticate themselves to each other
before IKE can proceed. Peer authentication occurs during the main mode/aggressive mode
exchange during IKE phase 1. The IKE protocol is very flexible and supports multiple
authentication methods as part of the phase 1 exchange. The two entities must agree on a
common authentication protocol through a negotiation process. IKE phase 1 has three
methods to authenticate IPSec peers in Cisco products: