ZyXEL Communications Prestige 652, User Manual, Page: 197 / 521

Prestige 652 Series User’s Guide
VPN Screens 17-13
17.10 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 17-4 Two 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 ( DH1 or DH2 ) .
Set the IKE SA lifetime. This field allows you to determine how long an IKE SA should stay up
before 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 which protocol to use ( ESP or AH ) for the IKE key exchange.
Choose an encryption algorithm.
Choose an authentication algorithm
Choose whether to enable Perfect Forward Secrecy (PFS) using Diffie-Hellman public-key
cryptography – see
section 17.10.3 . Select None (the default) to disable PFS.
Choose Tunnel mode or Transport mode.
Set the IPSec SA lifetime. This field allows you to determine how long the IPSec SA should
stay up before it times out. The Prestige automatically renegotiates the IPSec SA if there is
traffic when the IPSec SA lifetime period expires. The Prestige also automatically renegotiates
the IPSec SA if both IPSec routers have keep alive enabled, even if there is no traffic. If an
IPSec SA times out, then the IPSec router must renegotiate the SA the next time someone
attempts to send traffic.