As the initiator of an IKE SA, the router sends its IKE policies to the remote peer. If the peer has an IKE policy that matches the encryption, hash, authentication method, and Diffie-Hellmann group settings, the peer returns the matching policy. The peers use the lesser lifetime setting as the IKE SA lifetime. If no match is found, the IKE SA fails, and a log alarm is generated.
As the responder of an IKE negotiation, the router receives all IKE policies from a remote security gateway. The router then scans its own list of IKE policies to determine whether a match exists, starting from the highest priority. If it finds a match, that policy is successfully negotiated. Again, the lifetime is negotiated to the lesser of the two lifetimes, and failures are logged.