ZyXEL 202H 91-003-194001B User Manual

P-202H Plus v2 User’s Guide

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Chapter 11 VPN Screens

Figure 53   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 

. 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. 

The phase 1 Negotiation Mode you select determines how the Security Association (SA) will 
be established for each connection through IKE negotiations.