ZyXEL Communications P-334W - Manual (Page 227)

Prestige 334W User’s Guide
VPN Screens 16-17
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.
16.11.1 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.
16.11.2 Diffie-Hellman (DH) Key Groups
Diffie-Hellman (DH) is a public-key cryptography protocol that allows two parties to establish a shared
secret over an unsecured communications channel. Diffie-Hellman is used within IKE SA setup to establish
session keys. 768-bit (Group 1 - DH1) and 1024-bit (Group 2 – DH2) Diffie-Hellman groups are supported.
Upon completion of the Diffie-Hellman exchange, the two peers have a shared secret, but the IKE SA is not
authenticated. For authentication, use pre-shared keys.