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ZyWALL 10/50 Internet Security Gateway
VPN/IPSec Setup 26-13
Figure 26-8 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 IKE SA negotiation
should proceed before it times out. A value of 0 means IKE SA negotiation never times out. If
IKE SA negotiation times out, then both IKE SA and IPSec SA must be renegotiated.
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 26.5.5. 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 IPSec SA setup should
proceed before it times out. A value of 0 means IPSec SA never times out. If IPSec SA
negotiation times out, then the IPSec SA must be renegotiated (but not the IKE SA).
26.5.2 Negotiation Mode
The phase 1 Negotiation Mode you select determines how the Security Association (SA) will be established
for each connection through IKE negotiations.
Main Mode ensures the highest level of security when the communicating parties are
negotiating authentication (phase 1). It uses 6 messages in three round trips (SA negotiation,
Diffie-Hellman exchange and an exchange of nonces (a nonce is a random number)). This mode
features identity protection (your identity is not revealed in the negotiation).