User's Manual

Chapter 16 IPSec VPN 123
16.3.3 IKE Phases
There are two phases to every IKE (Internet Key Exchange) negotiation – phase 1 (Authentication)
and phase 2 (Key Exchange). A phase 1 exchange establishes an IKE SA and the second one uses
that SA to negotiate SAs for IPSec.
Figure 80 T
wo Phases to Set Up the IPSec SA
In phase 1 you must:
• Choose a negotiation mode.
• Authenticate the connection by entering a pre-shared key.
• Choose an encryption algorithm.
• Choose an authentication algorithm.
• Choose a Diffie-Hellman public-key cryptography key group.
• Set the IKE SA lifetime. This field allows you to determine how long an IKE SA should stay up
b
efore it times out. An IKE SA times out when the IKE SA lifetime period expires. If an IKE SA times
out when an IPSec SA is already established, the IPSec SA stays connected.
In phase 2 you must:
• Choose an encryption algorithm.
• Choose an authentication algorithm
• Choose a Diffie-Hellman public-key cryptography key group.
• Set the IPSec SA lifetime. This field allows you to determine how long the IPSec SA should stay up
b
efore it times out. The Router automatically renegotiates the IPSec SA if there is traffic when the
IPSec SA lifetime period expires. If an IPSec SA times out, then the IPSec router must renegotiate
the SA the next time someone attempts to send traffic.