Negotiation Mode - ZyXEL Communications P-660HN-51 User Manual

Figure 83 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 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
before it times out. The Zyxel Device 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.

13.4.4 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).
• Aggressive Mode is quicker than Main Mode because it eliminates several steps when the
communicating parties are negotiating authentication (phase 1). However the trade-off is that faster
speed limits its negotiating power and it also does not provide identity protection. It is useful in remote
access situations where the address of the initiator is not know by the responder and both parties
want to use pre-shared key authentication.
Chapter 13 IPSec
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