IKE Phase 1—Initially, a VPN peer will exchange the proposals for security services,
such as, encryption algorithms, authentication algorithm, hash function. Both the
VPN peers will form a security association which is a collection of parameters that
the two devices use. When both the VPN peers of the tunnel agree to accept a set of
security parameters, the IKE phase 1 is completed.
There are two modes in IKE
phase 1, main mode and aggressive mode.