User`s guide

Chapter 18 VPN Screens
P-2602HWUDL-D User’s Guide
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18.12 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 199 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 18.12.3 on page 285. 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 ZyXEL Device automatically renegotiates the
IPSec SA if there is traffic when the IPSec SA lifetime period expires. The ZyXEL Device
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.